Fix the 550 5.7.1 [SS] rejection

Your message was rejected with:

550 5.7.1 [SS] Message rejected

This means the subject line matched keywords strongly associated with spam. The 5.x.x code makes it a permanent failure — the message was returned, not queued for retry.

Common triggers are pharmaceutical and prescription drug names, sexually explicit wording, and phrasing typical of unsolicited bulk mail.

If you did not send it

Almost every case is a compromised mailbox: someone has your password and is sending through your account. Act on that first.

1. Change the mailbox password immediately — see Change your mailbox password. Use a long, unique password you do not use anywhere else.
2. Check for mail rules you did not create. Attackers commonly add a forwarder or a filter to hide the replies and bounces. Check cPanel → Email Filters and Forwarders.
3. Scan the computers that use the mailbox. Password-stealing malware is the usual way the credentials were taken in the first place, so changing the password without cleaning the machine just loses it again.
4. Update the operating system on those machines.

If you did send it

Reword the subject line and send again. The filter reads the subject, so a message about a legitimate topic that happens to use a flagged word will be rejected — a pharmacy, clinic or medical supplier sending genuine mail hits this regularly.

If your business legitimately needs to send such subjects, open a ticket rather than working around it, so we can look at your account specifically.

Getting sending restored

Once the password is changed and the machines are clean, open a ticket with your support PIN. Tell us what you changed. We can then review the account and lift the block.

Related

• Why are my emails being marked as spam?
• Get the full headers of an email
• Email sending limits