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Best practices for testing your emails through Postmark

Before you start sending emails to real users in your production environment, it’s always a good idea to start by sending test messages. You might even configure non-production environments to streamline the process of testing your emails. This gives you a safe environment to work out any kinks in your sending and how the emails look once they reach the inbox.

So how do you send test emails? Here are a few best practices to keep in mind to make testing your emails a little easier.

Sandbox Mode

Sandbox Mode allows you to safely test different parts of Postmark, such as bounces or webhooks, without sending to real recipients. Everything set up in a Sandbox Server will work the same way as a real Server, except for the actual email delivery, so you can fully test the application. Read more here on how to set up a Sandbox server, generate fake bounces, and more. 

Generate fake bounces using our blackhole domain

Postmark offers a black hole domain  ( which allows you to fully test out bounces with your integrations. Using our black hole domain will generate a fake bounce in your Postmark activity and trigger any connected webhooks, in the same way, a normal bounce works. It doesn’t count towards bounce limits or affect your sending reputation, so we would recommend this option over generating bounces to your own domain.

For each bounce type, we’ve set up a dedicated address to help you generate a fake bounce for it.

For example, if you’d like to create a hard bounce, you can send an email to It also supports camel case and is case insensitive, meaning also works. If you’re triggering a hard bounce, the fake bounce address is also added to the Stream’s Suppression list.

Other examples:

  • ISP Block:
  • Spam Notification:
  • Soft Bounce:

For a full list of all possible black hole addresses, check out our test bounces help doc.

Test a bounce email to your own domain

The most important thing to remember about testing emails is that the sending reputation of your production domain could be damaged if you’re not careful. If you send test emails from your production domain to fake addresses, or real addresses with low engagement, this can hurt the reputation of your domain and affect delivery in the future.

Please be aware that sending tests to your own domain, specifically in high volume that causes excessive bounces or low overall engagement can still hurt your overall deliverability. This is because mail providers like Google or Microsoft have "global" spam filters, so excessive bounces sent to your own domain can impact your overall sending.

We recommend Postmark's Sandbox or Fake bounce features to help avoid these possible negative deliverability consequences.

Best Practices

  • You could set up a mailbox on your domain like: and send all of your test emails there. Another option would be to set up a development subdomain domain like and have all of the test messages go there instead.
  • Use Using this for the recipient will send a test message that’s shown in Postmark’s Activity and Postmark will drop the message on our end. It’s also worth noting with this option that each email sent to that address will count towards your monthly limit.

Testing with the API

Postmark has a testing option you can use when sending via the API. We have a test API Token “POSTMARK_API_TEST” which you can use instead of your real API Token. This will allow you to make sure the API call you are using is valid and get a real response back. Using this method will not allow you to see the messages in your activity, nor will they get sent out, but it will tell you if your messages are being accepted. There’s also not a way to simulate a bounce with the Test API token.

Sending to multiple addresses

If your email provider supports aliases, you can use an alias of your email. For example, Gmail supports aliases so if your email address was then you could create a new user using the + symbol for an alias, like,,, etc. Postmark will register them as different email addresses, while emails will still go to the single inbox of

Last updated November 17th, 2022

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