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Moving from Postmark to mySMTP means updating your SMTP hostname, authentication method, and domain DNS records. This guide shows exactly what to change so nothing breaks during the transition.

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What changes

Your real mySMTP hostname is in your setup email. Do not use smtp.mysmtp.com.
Postmark uses message streams (identified by a header like X-PM-Message-Stream). mySMTP does not use message streams. Remove or replace any Postmark-specific headers in your code when switching to mySMTP.

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Before you cut over

  1. Export your suppression list from Postmark (bounces, spam complaints, unsubscribes). Do not send to those addresses from mySMTP. mySMTP does not import suppression lists automatically.
  2. Verify DNS for mySMTP. Add include:spf1.mysmtp.com to your existing SPF record (for example v=spf1 include:spf.mtasv.net include:spf1.mysmtp.com ~all) and add mySMTP DKIM TXT/CNAME records. Keep Postmark’s records in place until the transition is stable.
  3. Test connectivity with test.smtp.ai using your mySMTP credentials.

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Cutover steps

1

Update application SMTP settings

Replace Postmark’s smtp.postmarkapp.com with your mySMTP hostname, enter your mySMTP username and password, and use port 587 with STARTTLS.
2

Remove Postmark-specific headers

If your application sets X-PM-Message-Stream or other Postmark headers, remove or replace them. mySMTP does not require message stream headers.
3

Send test messages

Send a few test emails to addresses you control. Verify headers, authentication passes, and messages land in the inbox.
4

Monitor delivery metrics

Watch bounces, complaints, and inbox placement for 24 to 72 hours. Use the Email Header Analyzer in the mySMTP Deliverability Toolbox.
5

Warm up your dedicated IP

If you are on a dedicated IP plan (default), ramp volume gradually. See Warm up plans and use the warm-up generator.
6

Remove Postmark DNS records

Once sending is stable and your reputation metrics are good, remove include:spf.mtasv.net so your SPF record reads v=spf1 include:spf1.mysmtp.com ~all, and delete Postmark DKIM CNAME/TXT records.
mySMTP’s HTTP API is coming in Q4 2026. For now, switch to SMTP by updating your integration to use the settings in the table above. See Code examples for libraries in PHP, Python, Node.js, .NET, and Java.
Yes. Keep Postmark DNS records and credentials active while you warm up mySMTP. Only remove them after you confirm stable delivery.
No. You can keep the same from addresses and domains. Just make sure the domain’s SPF and DKIM include mySMTP.
If you did not export and exclude your Postmark suppression list, you may be mailing known bad addresses. Pause sending, clean your list, and resume with a smaller volume.