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You can read the introduction above and say: "Hey, we’ve always been testing our emailing using the corporate SMTP server and never went into issues! So, what’s wrong now?". Well, you’re lucky enough then. Actually I would point out several reasons why you shouldn’t do so:

Hence by using a dedicated mail server mock that is easily to configure and manage one may improve the reliability and effectiveness of testing email features.

In this example we’re download and run GreenMail email sandboxed mail server that supports SMTP, POP3, IMAP protocols and their TLS wrappers. We’ll concentrate on the first two protocols not to overwhelm the article.

We’ll see how to create user accounts at that server, how to send and receive emails with a popular Mozilla Thunderbird email client (the knowledge of how to manage things in Thunderbird is easily to transfer to any other email client).

There is the only prerequisite for you before you can start. The server is written in Java language so that you have to have JRE installed. The path to your JRE executable (in order to be able to run java command from anywhere) has to be present in PATH environment variable. Optionally you need to make sure that the ports you’re going to use for hosting email services are available and accessible from any required place of your network (otherwise you’ll only be able to work with the service using localhost loopback interface).

As I have mentioned before, GreenMail is a Java program. Thus, it is distributed as jar archive (a binary). It is worth saying that GreenMail is distributed in several different packages. Depending on your particular need, you can download binaries to use them as a part of your test solution so that you manage your server right from your code, or as a standalone solution so that you can run its self-sufficient executable archive. It can be available to more people, can be integrated with the tests, written in different languages (not only Java), take less time to start everything up, and in general have a higher degree of availability to everyone.

Since this article is related to #manual testing, we’re not going to manage everything from code. We’re not even going to write any line of code. We’ll be working with standalone package. You can find the latest builds at this official GreenMail download page. Download the binary that is against GreenMail Standalone, but don’t touch "Docker Hub" link. Save the downloaded jar file to some folder that is now to host our GreenMail server.

Now change current folder to one that you have chosen for storing executable jar of standalone package. Execute:

Where:

The command above will start some quick configuration of GreenMail that won’t have issues unless you either have mentioned ports occupied by some other processes or need to connect to your server from some outer machine. To fine-tune your server you will need to add more properties when execute the service.

If you are not satisfied with the ports which are assigned to the services when you set -Dgreenmail.setup.test.all property or you would like to connect to your mail stub from some different host of your network, then you can use more properties to set more specific port and host for each of service or not run some services at all.

If in some reason you need different ports to host your mail services, then you can combine the properties which are to address such goals. There are few things to remember:

The example above sets up default test configs for SMTP (-Dgreenmail.setup.test.smtp) and POP3 (-Dgreenmail.setup.test.pop3) protocols but overrides ip address binding (-Dgreenmail.hostname=0.0.0.0) so that both protocols are bound to default test ports but 0.0.0.0 ip address that allows to use them from outside. No other protocols except of mentioned two are started up.

The example above starts GreenMail that has two protocols enabled: SMTP that is started on 12345 port and POP3 that is sstarted on default test port 3110. Both are bound to 0.0.0.0 so that is is available from the outer network.

The example above shows the same case as previous one, but both the protocols are bound to 127.0.0.1 so that they can only be used from local host.

The example above demonstrates how to start GreenMail if you need only SMTP service that is to be available for only local connections

The example above runs SMTP and POP3 protocols which are both available for outer connections and which are both running on specific (non-default) ports.

GreenMail is a sandboxed service that is not intended to persist its state after shutting down. After all it is not fully featured email service but something that is extremely useful for testing. If you sent some mails and if you had some users on the server then everything will be lost after reboot. But how do we set up users on that server? There are two ways how the users appear in GreenMail.

First way is configuring users through a system property much like we can configure the protocols, ports, ans so on. There are several patterns for configuring users. I prefer to use this one:

The system property -Dgreenmail.users is just added to other properties which configure other aspects of your server. Despite you can create a user with only SMTP protocol enabled, for the further demonstration (connect with email client) we will need incoming email protocol also enabled. Hence with the following set of properties we can enable SMTP and POP3 protocols and set up some test account for them:

The example above will start SMTP and POP3 protocols available for only local connections and set up a user which has testacc account name that has testpwd password and that account is associated with testacc@webelement.click email.

Second way is when you send an email to someone that does not exist on the server. If the email is sent through SMTP service of GreenMail, and there is no associated account for that email, then the account is created automatically. In that way account name is just equal to the email address (unlike the previous approach where account name and email are different things). The password in turn is the same as the account name and obviously the same as email address. We’ll take a look at that more closely in the next chapter.

Your tests wouldn’t be reliable and effective if you wouldn’t be able to send and receive emails through some email client. In this paragraph we’re going to use Mozilla Thunderbird in order to connect to GreenMail, send and receive emails. We’ll also demonstrate how new users are created in end-to-end flow.

Here I assume that you have Thunderbird already installed so that we do not start from scratch. Lets run both SMTP and POP3 protocols (local connections would be enough for the demo) as we have done that in previous examples:

Here you should see some output if you are not detaching your console from the executed server (I believe that if you carefully followed my examples then you are not). The output is informative enough despite it is not in verbose mode (that can be enabled with dedicated system property). From the output we can find out which protocols are executed on which ports and bound to which ip addresses. Now we can configure our mail client to work with the running instance of GreenMail.

Click [Email] button under "Set up an account". There you will see the dialog to configure your email account. What you will see is actually implies that Thunderbird will do everything automatically for you, however we do not have a real email infrastructure so that we’ll have to configure everything manually. Type in your name, account name, email and password. You can set any name, but you have to set other fields corresponding to what we set up when executed our server. Remember, account name is testacc, password is testpwd and email is testacc@webelement.click. After you have set up everything click [Manual config] button.

Now you can specify our custom connectivity settings. The only fields you need to change is what is outlined with orange line. Change incoming protocol to POP3, change server hostnames for both the protocols to localhost, change the ports to the ones we specified when executed our server: 54321 for POP3 and 12345 for SMTP. Click [Re-test] button. SSL and Authentication properties will be queried from our server and set up automatically.

Now click [Done] button. You should see the warning saying that the server does not use SSL encryption. Check "I understand the risk" checkbox and then [Done] button. You now have completed account configuration for your testacc account. You can send and receive messages.

If you click [Get Messages] button nothing will be downloaded because neither a human nor a process sent anything to your new account. Let’s write some email to non-existent address.

Click [Write] button. You will see email editor. Set some non-existent address to To: field. For example that address could be testacc@webelement.pleasedontclick. Set some subject and write some text in body. Then click [Send] button. If you look to the console window where you started GreenMail server, you should see something like this:

"Created user login testacc@webelement.pleasedontclick for address testacc@webelement.pleasedontclick with password testacc@webelement.pleasedontclick because it didn’t exist before"

This means that we can repeat the steps we were doing for our testacc with some small difference. That time our account name was what preceded @ symbol. Now there is different case. The whole email address is the account name, hence we have to change some more fields this time, like it is shown below:

Fields which are pointed with the arrows (plus the email field itself) have to contain the account email (i.e. testacc@webelement.pleasedontclick) as their values. Once you have confirmed all the further dialogs you will see that you now have one more account set up in your Thunderbird client. You will also see that there is one email in inbox folder of your new account. That email is exactly what we have recently sent to it.

Now you know how to set up test email infrastructure so that you’re not under the risk of data leakage or other harmful impact on your company or your customers. If you still have the questions please send them to me using this form. I will amend the article according to your feedback.