Complete guide to email verifications with Automation SMTP Server

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Post summary: How to do complete email verification with your own Automation SMTP server.

SMTP is protocol initially defined in 1982 and is still used nowadays. In order to automate application which sends out emails, you need SMTP server which reads messages and saves them to disk for further processing. Note that this is only in the case when your application sends emails.

Windows SMTP server

One option is to use SMTP server provided by Windows. Problems here are two. First is that from Vista SMTP server is no more supported. There is SMTP server in Windows Server distributions but the license for them is more expensive. The second problem comes from the configuration of the server. You might have several machines and configurations should be maintained on all of them. It is a feasible option to use Windows SMTP server but the current post is not dedicated to it.

Automation SMTP Server

What I offer in this post is your own Automation SMTP Server. It is located in following GitHub project. The solution is actually a mixture of two open source projects. For the server, I use Antix SMTP Server For Developers, which is really good SMTP server. It is windows application and is more suitable for manual SMTP testing rather than automation. I’ve extracted the SMTP core with some modifications as a console application which saves emails as EML file on disk. For the reading of emails, I use the source code of Easily Retrieve Email Information from .EML Files article with several modifications. What you need to do in order to make successful email verification is download executable from GitHub and follow instructions below. More info for it can be found on its homepage Automation SMTP Server.

Automation SMTP Server usage

In GitHub AutomationSMTPServer repository there is an example that shows how to use Automation SMTP Server. The server should be added as a reference to your automation project. Since it is a reference it gets copied into compiled executables folder.

Delete recent emails

Before doing anything in your tests it is good to delete old emails. Automation SMTP Server is saving mail into a folder named “temp”. This is how it works and cannot be changed.

private string currentDir =
	Directory.GetCurrentDirectory() + Path.DirectorySeparatorChar;
private string mailsDir = currentDir + "temp";

if (Directory.Exists(mailsDir))
	Directory.Delete(mailsDir, true);

Start Automation SMTP Server

The server is a console application. It receives emails and saves them to disk. If counterparty sends a QUIT message to disconnect server gets restarted to wait for next connection. The server should be started as a process. Port should be provided as arguments. If not provided it can be configured in SMTP Server config file. If not configured there it gives a message and takes 25 for default port.

Process smtpServer = new Process();
smtpServer.StartInfo.FileName = currentDir + "AutomationSMTPServer.exe";
smtpServer.StartInfo.Arguments = "25";

Send emails

This is the point where your application under test is sending emails which you will later verify.

Read emails

Once emails have been sent out from the application under test you are ready to read and process them.

string[] files = Directory.GetFiles(mailsDir);
List<EMLFile> mails = new List<EMLFile>();

foreach (string file in files)
	EMLFile mail = new EMLFile(file);

Verify emails

Here you can use EMLFile class which is parsing the EML file and is representing is an object so you can do operations on it. Once you have the mail as an object you can access all its attributes and verify some of them. It all depends on your testing strategy. Another option is to define on expected EML file, read it and compare both actual and expected. EMLFile class has predefined Equals method which is comparing all the attributes of the emails.

bool compare1 = mails[0].Equals(mails[1]);
bool compare2 = mails[0].Equals(mails[2]);
bool compare3 = mails[1].Equals(mails[2]);

Stop Automation SMTP Server

This part is important. If not stopped server will continue to work and will block the port. Its architecture is defined in such manner that only way to stop it is it to terminate console application. In a case where you have started it from C# code as process way to stop it is to kill the process.



Proper email verification can be a challenge. In case your application under tests send emails I would say it is crucial to have correct email testing as mail is what customers receive. And in the end, it is all about customers! So give it a try and enjoy this easy way of email verification.