Using mabl Mailbox

This guide provides an overview of how to create a mabl Mailbox address and use it for email testing.

Generating a mabl Mailbox address

To get started, create or edit a browser test in the mabl Trainer. Then take the following steps:

  1. Click on the {x} icon at the bottom of the Trainer window.
  2. Click on Create a new variable.
  3. Select mabl mailbox address as the source.
  4. Give your mabl Mailbox variable a name.
  5. Click OK. You've just created a mabl Mailbox variable!

Creating a Mailbox email address


Custom Email Prefixes

You can also use custom email address prefixes to distinguish your emails.

Using a mabl Mailbox address in a form

After creating a mabl mailbox address, you can test it out! In the example below, we use the mabl Mailbox sandbox:

  1. Click on the {x} icon at the bottom of the Trainer window.
  2. Click on Use an existing variable.
  3. Click on the input element where you wish to insert the mabl mailbox address.
  4. Select the mabl mailbox variable from the dropdown.
  5. Click OK. The mabl mailbox address will be inserted into the input field you selected.

Insert the Mailbox email address into a submission form

Once you submit your form and send the email, the message will appear in the Mailbox email assertions menu.

Creating an email assertion

The next step is to check whether the email has been received:

  1. Click on the check mark icon at the bottom of the Trainer window.
  2. Select Email. It may take a minute for the email to arrive from your email server. Use the refresh button on the mail screen to check for new mail.
  3. Click on the email of interest to open the assertion menu. You may assert against the sender address or the email subject. Additional options include disable case sensitivity and continue on failure.

Asserting against email properties

Opening an email

You can interact with the received email and follow links as if it were a typical web page. To open an email sent to a mabl Mailbox email address, take the following steps:

  1. Click on the plus icon at the bottom of the mabl Trainer window to add a step.
  2. Select the Mailbox step. You will see the emails that have been sent to your mabl mailbox.
  3. Hover over the email that you'd like to open.
  4. Click on the open email icon that appears.

Now you can interact with the rendered email as if it were any other webpage.


Open the rendered email and interact with it, including clicking through links.

Verifying attachments

When viewing and interacting with the rendered email, you also have the ability to verify attachments to ensure that you're able to test every part of an email. Mabl Mailbox supports:

  • Inline attachments (Inline attachments are intended to be part of the email body).
  • Regular Attachments


Note on attachment size

The total email size must be less than 10 MiB. Since this includes all email headers and metadata, the attachment limit is also under 10 MiB.

Click on the link to the attachment to download it. Mabl will automatically download the attachment and let you assert on it normally, as you would with any other download.


The location of attachments within a mabl Mailbox rendered email.


Multiple matches

If your email selector matches multiple emails from the same Mailbox delivery address or subject line, mabl will open the most recently delivered matching email.

If the attachment is a PDF, and your subscription (i.e. Enterprise) includes PDF support, mabl will ask if you would like to test the PDF. From here you can test your PDF as you would any other.


Attachment expiration

Attachment links will expire after 1 hour. If you keep an email validation tab open during manual training for over an hour, the links will not resolve. If you need to refresh the attachment links, you can replay the trained test.

Exploring the Mailbox sandbox

Interested in learning more about mabl Mailbox? We recommend testing against the mabl sandbox app, which has a dedicated Mailbox section. To start trying it out, you can add an email address, subject, and body.


Mabl sandbox Mailbox example