Verifalia 4.2.0

dotnet add package Verifalia --version 4.2.0                
NuGet\Install-Package Verifalia -Version 4.2.0                
This command is intended to be used within the Package Manager Console in Visual Studio, as it uses the NuGet module's version of Install-Package.
<PackageReference Include="Verifalia" Version="4.2.0" />                
For projects that support PackageReference, copy this XML node into the project file to reference the package.
paket add Verifalia --version 4.2.0                
#r "nuget: Verifalia, 4.2.0"                
#r directive can be used in F# Interactive and Polyglot Notebooks. Copy this into the interactive tool or source code of the script to reference the package.
// Install Verifalia as a Cake Addin
#addin nuget:?package=Verifalia&version=4.2.0

// Install Verifalia as a Cake Tool
#tool nuget:?package=Verifalia&version=4.2.0                

Verifalia API NuGet License

Verifalia RESTful API - .NET SDK and helper library

Verifalia provides a simple HTTPS-based API for validating email addresses in real-time and checking whether they are deliverable or not; this SDK library integrates with Verifalia and allows to verify email addresses under the following platforms:

  • .NET 5.0 and higher, including .NET 8.0 new
  • .NET Core 1.0 (and higher)
  • .NET Framework 4.5 (and higher)
  • .NET Standard 1.3 (and higher)
    • Mono 4.6+
    • Xamarin.iOS 10.0+
    • Xamarin.Mac 3.0+
    • Xamarin.Android 7.0+
    • Universal Windows Platform 10.0+

To learn more about Verifalia please see

Table of contents

Adding Verifalia REST API support to your .NET solution

The best and easiest way to add the Verifalia email verification SDK library to your .NET project is to use the NuGet package manager.

With Visual Studio IDE

From within Visual Studio, you can use the NuGet GUI to search for and install the Verifalia NuGet package. Or, as a shortcut, simply type the following command into the Package Manager Console:

Install-Package Verifalia
Manual download and compilation

As an alternative way to add the Verifalia SDK to your .NET solution, you can download the SDK source project from github, extract it to a folder of your choice and add a reference from your own project to the Verifalia SDK project. The SDK project is a C# project which can be referenced and used with any other .NET language too, including Visual Basic (VB.NET), C++/CLI, J#, IronPython, IronRuby, F# and PowerShell.

Learn more at


First things first: authentication to the Verifalia API is performed by way of either the credentials of your root Verifalia account or of one of its users (previously known as sub-accounts): if you don't have a Verifalia account, just register for a free one. For security reasons, it is always advisable to create and use a dedicated user for accessing the API, as doing so will allow to assign only the specific needed permissions to it.

Learn more about authenticating to the Verifalia API at

Once you have your Verifalia credentials at hand, use them while creating a new instance of the VerifaliaRestClient type, which will be the starting point to every other operation against the Verifalia API: the supplied credentials will be automatically provided to the API using the HTTP Basic Auth method.

using Verifalia.Api;

var verifalia = new VerifaliaRestClient("username", "password");

In addition to the HTTP Basic Auth method, this SDK also supports other different ways to authenticate to the Verifalia API, as explained in the subsequent sections.

Authenticating via bearer token

Bearer authentication offers higher security over HTTP Basic Auth, as the latter requires sending the actual credentials on each API call, while the former only requires it on a first, dedicated authentication request. On the other side, the first authentication request needed by Bearer authentication takes a non-negligible time: if you need to perform only a single request, using HTTP Basic Auth provides the same degree of security and is also faster.

using Verifalia.Api;
using Verifalia.Api.Security;

var verifalia = new VerifaliaRestClient(new BearerAuthenticationProvider("username", "password"));

Handling multi-factor auth (MFA) is also possible by defining a custom implementation of the ITotpTokenProvider interface, which should be used to acquire the time-based one-time password from an external authenticator app or device: to add multi-factor auth to your root Verifalia account, configure your security settings.

using Verifalia.Api;
using Verifalia.Api.Security;

class MyTotpProvider : ITotpTokenProvider
	public Task<string> ProvideTotpTokenAsync(CancellationToken cancellationToken)
		// Ask the user to type his or her TOTP token

		Console.WriteLine("Acquire your TOTP token and type it here:");
		var totpToken = Console.ReadLine();

		return Task.FromResult(totpToken);

// ...

var verifalia = new VerifaliaRestClient(new BearerAuthenticationProvider("username", "password", new MyTotpProvider()));
Authenticating via X.509 client certificate (TLS mutual authentication)

This authentication method uses a cryptographic X.509 client certificate to authenticate against the Verifalia API, through the TLS protocol. This method, also called mutual TLS authentication (mTLS) or two-way authentication, offers the highest degree of security, as only a cryptographically-derived key (and not the actual credentials) is sent over the wire on each request.

using Verifalia.Api;
using Verifalia.Api.Security;

var verifalia = new VerifaliaRestClient(new X509Certificate2("mycertificate.pem"));

Validating email addresses

Every operation related to verifying / validating email addresses is performed through the EmailValidations property exposed by the VerifaliaRestClient instance you created above. The property is filled with useful methods, each one having lots of overloads: in the next few paragraphs we are looking at the most used ones, so it is strongly advisable to explore the library and look at the embedded xmldoc help for other opportunities.

The library automatically waits for the completion of email verification jobs: if needed, it is possible to adjust the wait options and have more control over the entire underlying polling process. Please refer to the Wait options section below for additional details.

How to validate an email address

To validate an email address from a .NET application you can invoke the SubmitAsync() method: it accepts one or more email addresses and any eventual verification options you wish to pass to Verifalia, including the expected results quality, deduplication preferences, processing priority.

Note In the event you need to verify a list of email addresses, it is advisable to submit them all at once through one of the dedicated SubmitAsync() method overloads (see the next sections), instead of iterating over the source set and submitting the addresses one by one. Not only the all-at-once method would be faster, it would also allow to detect and mark duplicated items - a feature which is unavailable while verifying the email addresses one by one.

In the following example, we verify an email address with this library, using the default options:

var job = await verifalia

// At this point the address has been validated: let's print its email validation
// result to the console.

var entry = job.Entries[0];

Console.WriteLine($"Classification: {entry.Classification} (status: {entry.Status})");

// Classification: Deliverable (status: Success)

As you may expect, each entry may include various additional details about the verified email address:

Property Description
AsciiEmailAddressDomainPart Gets the domain part of the email address, converted to ASCII if needed and with comments and folding white spaces stripped off.
Classification The ValidationEntryClassification value for this entry.
CompletedOn The date this entry has been completed, if available.
Custom A custom, optional string which is passed back upon completing the validation. To pass back and forth a custom value, use the Custom property of ValidationRequestEntry.
DuplicateOf The zero-based index of the first occurrence of this email address in the parent Validation, in the event the Status for this entry is Duplicate; duplicated items do not expose any result detail apart from this and the eventual Custom values.
Index The index of this entry within its Validation container; this property is mostly useful in the event the API returns a filtered view of the items.
InputData The input string being validated.
EmailAddress Gets the email address, without any eventual comment or folding white space. Returns null if the input data is not a syntactically invalid e-mail address.
EmailAddressDomainPart Gets the domain part of the email address, without comments and folding white spaces.
EmailAddressLocalPart Gets the local part of the email address, without comments and folding white spaces.
HasInternationalDomainName If true, the email address has an international domain name.
HasInternationalMailboxName If true, the email address has an international mailbox name.
IsDisposableEmailAddress If true, the email address comes from a disposable email address (DEA) provider. <a href="">What is a disposable email address?</a>
IsFreeEmailAddress If true, the email address comes from a free email address provider (e.g. gmail, yahoo, outlook / hotmail, ...).
IsRoleAccount If true, the local part of the email address is a well-known role account.
Status The ValidationEntryStatus value for this entry.
Suggestions The potential corrections for the input data, in the event Verifalia identified potential typos during the verification process.
SyntaxFailureIndex The position of the character in the email address that eventually caused the syntax validation to fail.

Here is another example, showing some of the additional result details provided by Verifalia:

var job = await verifalia

var entry = job.Entries[0];

Console.WriteLine($"Classification: {entry.Classification}");
Console.WriteLine($"Status: {entry.Status}");
Console.WriteLine($"Syntax failure index: {entry.SyntaxFailureIndex}");

if (entry.Suggestions != null)

    foreach (var suggestion in entry.Suggestions)
        Console.WriteLine($"- {suggestion}");

// Classification: Undeliverable
// Status: InvalidCharacterInSequence
// Syntax failure index: 3
// Suggestions:
// -

How to validate a list of email addresses

To verify a list of email addresses - instead of a single address - it is possible to use the SubmitAsync() method overload which accepts an IEnumerable<string>; if the email addresses to be verified are originally stored in a file, it is also possible to simply upload the file and have Verifalia automatically import and verify it - see the next section for the details.

Here is an example showing how to verify an array with some email addresses:

var job = await verifalia
    .SubmitAsync(new[] {

Console.WriteLine($"Job ID: {job.Overview.Id}");

foreach (var entry in job.Entries)
    Console.WriteLine($"- {entry.InputData} => {entry.Classification} ({entry.Status})");

// Job Id: 290b5146-eeac-4a2b-a9c1-61c7e715f2e9
// - => Deliverable (Success)
// - => Undeliverable (DomainIsMisconfigured)
// - => Deliverable (Success)

How to import and submit a file for validation

This library includes support for submitting and validating files with email addresses, including:

  • plain text files (.txt), with one email address per line;
  • comma-separated values (.csv), tab-separated values (.tsv) and other delimiter-separated values files;
  • Microsoft Excel spreadsheets (.xls and .xlsx).

To submit and validate files, one can still use the SubmitAsync() method mentioned above, passing either a Stream or a FileInfo instance or just a byte[] with the file content. Along with that, it is also possible to specify the eventual starting and ending rows to process, the column, the sheet index, the line ending and the delimiter - depending of course on the nature of the submitted file (see FileValidationRequest in the source to learn more).

Here is how to submit and verify an Excel file, for example:

var job = await verifalia
    .SubmitAsync(new FileInfo("that-file.xslx"));

For more advanced options, just pass FileValidationRequest instance to the SubmitAsync() method:

var job = await verifalia
    .SubmitAsync(new FileValidationRequest(new FileInfo("that-file.xslx"))
            Sheet = 3,
            StartingRow = 1,
            Column = 5
        quality: QualityLevelName.High);

And here is another example, showing how to submit a Stream instance and specifying the MIME content type of the file, which is automatically determined from the file extension in the event you pass a FileInfo instance:

Stream inputStream = ...; // TODO: Acquire the input data somehow

var job = await verifalia
        MediaTypeHeaderValue.Parse(WellKnownMimeContentTypes.TextPlain)); // text/plain

Processing options

While submitting one or more email addresses for verification, it is possible to specify several options which affect the behavior of the Verifalia processing engine as well as the verification flow from the API consumer standpoint.

Quality level

Verifalia offers three distinct quality levels - namely, Standard, High and Extreme - which rule out how the email verification engine should deal with temporary undeliverability issues, with slower mail exchangers and other potentially transient problems which can affect the quality of the verification results. The SubmitAsync() method overloads accept a quality parameter which allows to specify the desired quality level; here is an example showing how to verify an email address using the High quality level:

var job = await verifalia
    .SubmitAsync("", quality: QualityLevelName.High);
Deduplication mode

The SubmitAsync() method overloads accepting multiple email addresses at once allow to specify how to deal with duplicated entries pertaining to the same input set; Verifalia supports a Safe deduplication mode, which strongly adheres to the old IETF standards, and a Relaxed mode which is more in line with what can be found in the majority of today's mail exchangers configurations.

In the next example, we show how to import and verify a list of email addresses and mark duplicated entries using the Relaxed deduplication mode:

var job = await verifalia
    .SubmitAsync(new FileInfo("that-file.xslx"), deduplication: DeduplicationMode.Relaxed);
Data retention

Verifalia automatically deletes completed email verification jobs according to the data retention policy defined at the account level, which can be eventually overriden at the user level: one can use the Verifalia clients area to configure these settings.

It is also possible to specify a per-job data retention policy which govern the time to live of a submitted email verification job; to do that, use the SubmitAsync() method overloads which either accepts a ValidationRequest or a FileValidationRequest instance and initialize its Retention property accordingly.

Here is how, for instance, one can set a data retention policy of 10 minutes while verifying an email address:

var job = await verifalia
    .SubmitAsync(new ValidationRequest(new[]
        Retention = TimeSpan.FromMinutes(10)

Wait options

By default, the SubmitAsync() method overloads submit an email verification job to Verifalia and wait for its completion; the entire process may require some time to complete depending on the plan of the Verifalia account, the number of email addresses the submission contains, the specified quality level and other network factors including the latency of the mail exchangers under test.

In waiting for the completion of a given email verification job, the library automatically polls the underlying Verifalia API until the results are ready; by default, it tries to take advantage of the long polling mode introduced with the Verifalia API v2.4, which allows to minimize the number of requests and get the verification results faster.

Avoid waiting

In certain scenarios (in a microservice architecture, for example), however, it may preferable to avoid waiting for a job completion and ask the Verifalia API, instead, to just queue it: in that case, the library would just return the job overview (and not its verification results) and it will be necessary to retrieve the verification results using the GetAsync() method.

To do that, it is possible to specify the WaitOptions.NoWait as the value for the waitOptions parameter of the SubmitAsync() method overloads, as shown in the next example:

var job = await verifalia
    .SubmitAsync(new FileInfo("that-file.xslx"),
        waitOptions: WaitOptions.NoWait);

Console.WriteLine($"Status: {job.Overview.Status}");
// Status: InProgress
Progress tracking

For jobs with a large number of email addresses, it could be useful to track progress as they are processed by the Verifalia email verification engine; to do that, it is possible to create an instance of the WaitOptions class and provide an handler which eventually receives progress notifications through the Progress property.

Here is how to define a progress notification handler which displays the progress percentage of a submitted job to the console window:

var job = await verifalia
    .SubmitAsync(new FileInfo("that-other-file.csv"),
        waitOptions: new WaitOptions
            Progress = new Progress<ValidationOverview>(overview =>

Completion callbacks

Along with each email validation job, it is possible to specify an URL which Verifalia will invoke (POST) once the job completes: this URL must use the HTTPS or HTTP scheme and be publicly accessible over the Internet. To learn more about completion callbacks, please see

To specify a completion callback URL, pass either a ValidationRequest or a FileValidationRequest to the SubmitAsync() method and set its CompletionCallback property accordingly, as shown in the example below:

await verifalia
    .SubmitAsync(new ValidationRequest(new[] { "" })
        CompletionCallback = new CompletionCallback("https://your-website-here/foo/bar")

Note that completion callbacks are invoked asynchronously and it could take up to several seconds for your callback URL to get invoked.

Retrieving jobs

It is possible to retrieve a job through the GetAsync() and GetOverviewAsync() methods, which return, respectively, a Validation instance or a ValidationOverview instance for the desired email verification job. While doing that, the library automatically waits for the completion of the job, and it is possible to adjust this behavior by passing to the aforementioned methods a waitOptions parameter, in the exactly same fashion as described for the SubmitAsync() method overloads; please see the Wait options section for additional details.

Here is an example showing how to retrieve a job, given its identifier:

var jobId = Guid.Parse("ec415ecd-0d0b-49c4-a5f0-f35c182e40ea");
var job = await verifalia.EmailValidations.GetAsync(jobId);

Exporting email verification results in different output formats

This library also allows to export the entries of a completed email validation job in different output formats through the ExportEntriesAsync() method, with the goal of generating a human-readable representation of the verification results.

WARNING: While the output schema (columns / labels / data format) is fairly complete, you should always consider it as subject to change: use the GetAsync() / GetEntriesAsync() methods instead if you need to rely on a stable output schema.

Here is an example showing how to export a given email verification job as a comma-separated values (CSV) file:

// Exports the validated entries for the job in the CSV format

var exportedStream = await verifalia
    .ExportEntriesAsync(new Guid("722c2fd8-8837-449f-ad24-0330c597c993"),

// Creates the output file stream

var fileStream = new FileStream("my-list.csv", FileMode.Create);

// Copies the exported stream into the output file stream

await exportedStream.CopyToAsync(fileStream);

Don't forget to clean up, when you are done

Verifalia automatically deletes completed jobs after a configurable data-retention policy (see the related section) but it is strongly advisable that you delete your completed jobs as soon as possible, for privacy and security reasons. To do that, you can invoke the DeleteAsync() method passing the job Id you wish to get rid of:

await verifalia

Once deleted, a job is gone and there is no way to retrieve its email validation results.

Iterating over your email validation jobs

For management and reporting purposes, you may want to obtain a detailed list of your past email validation jobs. This SDK library allows to do that through the ListAsync() method, which allows to iterate asynchronously over a collection of ValidationOverview instances (the same type of the Overview property of the results returned by SubmitAsync() and GetAsync()).

Here is how to iterate over your jobs, from the most recent to the oldest one:

var jobOverviews = verifalia
    .ListAsync(new ValidationOverviewListingOptions
        Direction = Direction.Backward

await foreach (var jobOverview in jobOverviews)
    Console.WriteLine("Id: {0}, status: {2}, entries: {3}",

// Prints out something like:
// Id: a7784f9a-86d4-436c-b8e4-f72f2bd377ac, status: InProgress, entries: 9886
// Id: 86d57c00-147a-4736-88cc-c918260c67c6, status: Completed, entries: 1
// Id: 594bbb0f-6f12-481c-926f-606cfefc1cd5, status: Completed, entries: 1
// Id: a5c1cd5b-39cc-43bc-9a3a-ee4a0f80ee6d, status: InProgress, entries: 226
// Id: b6f69e30-60dd-4c21-b2cb-e73ba75fb278, status: Completed, entries: 12077
// Id: 5e5a97dc-459f-4edf-a607-47371c32aa94, status: Deleted, entries: 1009
// ...

The ListAsync() method uses the C# 8.0 async enumerable feature; for previous language support please check the ListSegmentedAsync() methods group.

Filtering email validation jobs

The ListAsync() method also have the ability, by way of the same options argument, to filter the email verification jobs returned by the Verifalia API: it is possible to filter by date of submission, owner and status of the jobs.

Here is how to repeat the listing operation shown in the example above, this time returning only the jobs of a given user and for a given date range:

var jobOverviews = verifalia
    .ListAsync(new ValidationOverviewListingOptions
        Direction = Direction.Backward,
        CreatedOn = new DateBetweenPredicate(new DateTime(2024, 1, 3),
            new DateTime(2024, 1, 7)),
        Owner = new StringEqualityPredicate("50173acd-9ed2-4298-ba7f-8ccaeed48deb")

await foreach (var jobOverview in jobOverviews)
    // ...

Managing credits

To manage the Verifalia credits for your account you can use the Credits property exposed by the VerifaliaRestClient instance created above. Like for the previous topic, in the next few paragraphs we are looking at the most used operations, so it is strongly advisable to explore the library and look at the embedded xmldoc help for other opportunities.

Getting the credits balance

One of the most common tasks you may need to perform on your account is retrieving the available number of free daily credits and credit packs. To do that, you can use the GetBalanceAsync() method, which returns a Balance object, as shown in the next example:

var balance = await verifalia

Console.WriteLine("Credit packs: {0}, free daily credits: {1} (will reset in {2})",

// Prints out something like:
// Credit packs: 956.332, free daily credits: 128.66 (will reset in 09:08:23)

To add credit packs to your Verifalia account visit

Retrieving credits usage statistics

As a way to monitor and forecast the credits consumption for your account, the method ListDailyUsagesAsync() allows to retrieve statistics about historical credits usage, returning an asynchronously iterable collection of DailyUsage instances. The method also allows to limit the period of interest by passing a DailyUsageListingOptions instance. Elements are returned only for the dates where consumption (either of free credits, credit packs or both) occurred.

Here is how to retrieve the daily credits consumption for the last thirty days:

var dailyUsages = verifalia
    .ListDailyUsagesAsync(new DailyUsageListingOptions
        DateFilter = new DateBetweenPredicate
            Since = DateTime.Now.AddDays(-30)

await foreach (var dailyUsage in dailyUsages)
    Console.WriteLine("{0:yyyyMMdd} - credit packs: {1}, free daily credits: {2}",

// Prints out something like:
// 20240201 - credit packs: 1965.68, free daily credits: 200
// 20240126 - credit packs: 0, free daily credits: 185.628
// 20240125 - credit packs: 15.32, free daily credits: 200
// ...

The ListDailyUsagesAsync() method uses the C# 8.0 async enumerable feature; for previous language support please check the ListDailyUsagesSegmentedAsync() methods group.

Changelog / What's new

This section lists the changelog for the current major version of the library: for older versions, please see the project releases.


Released on January 11<sup>th</sup>, 2024

  • Added support for API v2.5
  • Added support for classification override rules
  • Added support for AI-powered suggestions
  • Added support for .NET 8.0
  • Bumped dependencies


Released on May 26<sup>th</sup>, 2023

  • Added support for filters when listing email verification jobs
  • Resolved an issue with the ToAsyncEnumerableAsync() method that previously resulted in incomplete listings in specific scenarios


Released on February 27<sup>th</sup>, 2023

  • Added support for API v2.4
  • Added support for .NET 7.0
  • Added support for new completion callback options
  • Added support for parked mail exchangers detection
  • Added support for specifying a custom wait time while submitting and retrieving email verification jobs
  • Added support for nullable annotations
  • Breaking change: renamed WaitingStrategy into WaitOptions and refactored the latter so that it now allows to adjust the underlying polling wait times
  • Breaking change: the default job submission and retrieval behavior is now to wait for the completion of jobs (but it is possible to change that through the new WaitOptions class)
  • Breaking change: the CompletionCallback property of the ValidationRequest and FileValidationRequest classes now points to a full fledged CompletionCallback class instead of a simple Uri
  • Bumped dependencies (including Newtonsoft.Json and Flurl)
  • Improved documentation
Product Compatible and additional computed target framework versions.
.NET net5.0 is compatible.  net5.0-windows was computed.  net6.0 is compatible.  net6.0-android was computed.  net6.0-ios was computed.  net6.0-maccatalyst was computed.  net6.0-macos was computed.  net6.0-tvos was computed.  net6.0-windows was computed.  net7.0 is compatible.  net7.0-android was computed.  net7.0-ios was computed.  net7.0-maccatalyst was computed.  net7.0-macos was computed.  net7.0-tvos was computed.  net7.0-windows was computed.  net8.0 is compatible.  net8.0-android was computed.  net8.0-browser was computed.  net8.0-ios was computed.  net8.0-maccatalyst was computed.  net8.0-macos was computed.  net8.0-tvos was computed.  net8.0-windows was computed. 
.NET Core netcoreapp1.0 is compatible.  netcoreapp1.1 is compatible.  netcoreapp2.0 is compatible.  netcoreapp2.1 is compatible.  netcoreapp2.2 is compatible.  netcoreapp3.0 is compatible.  netcoreapp3.1 is compatible. 
.NET Standard netstandard1.3 is compatible.  netstandard1.4 is compatible.  netstandard1.5 is compatible.  netstandard1.6 is compatible.  netstandard2.0 is compatible.  netstandard2.1 is compatible. 
.NET Framework net45 is compatible.  net451 is compatible.  net452 is compatible.  net46 is compatible.  net461 is compatible.  net462 is compatible.  net463 was computed.  net47 is compatible.  net471 is compatible.  net472 is compatible.  net48 is compatible.  net481 was computed. 
MonoAndroid monoandroid was computed. 
MonoMac monomac was computed. 
MonoTouch monotouch was computed. 
Tizen tizen30 was computed.  tizen40 was computed.  tizen60 was computed. 
Universal Windows Platform uap was computed.  uap10.0 was computed. 
Xamarin.iOS xamarinios was computed. 
Xamarin.Mac xamarinmac was computed. 
Xamarin.TVOS xamarintvos was computed. 
Xamarin.WatchOS xamarinwatchos was computed. 
Compatible target framework(s)
Included target framework(s) (in package)
Learn more about Target Frameworks and .NET Standard.

NuGet packages

This package is not used by any NuGet packages.

GitHub repositories

This package is not used by any popular GitHub repositories.

Version Downloads Last updated
4.2.0 45,902 1/11/2024
4.1.0 5,718 5/26/2023
4.0.0 70,896 2/27/2023
3.1.0 176,085 12/2/2021
3.0.0 63,814 1/22/2021
2.4.0 7,507 11/20/2020
2.3.0 398 11/13/2020
2.2.0 900 2/21/2020
2.1.0 1,205 11/22/2019
2.0.2 59,690 8/23/2019
2.0.1 659 8/3/2019
2.0.0 603 8/2/2019
1.8.1 171,568 8/18/2017
1.7.0 9,861 6/29/2017