550 5.7.27: SPF failed for a bulk sender (Gmail)
At Gmail, this code means your message failed SPF and Gmail requires bulk senders to pass SPF. Other mail servers use the same code for a different, rarer problem: your From domain publishes a "null MX" record, which says it never receives email.
Blocked The address is probably fine. The problem is how the mail was sent.
What the bounce message looks like
The wording changes from one provider to another. These are typical examples:
550 5.7.27 This message was blocked because it didn't pass SPF authentication. Gmail requires bulk email senders to authenticate their email with SPF. (Gmail)550 5.7.27 Sender address has null MX (other servers)Common causes
- No SPF record on the sending domain
- Your email service isn't included in your SPF record
- More than one SPF record, or too many DNS lookups
- Less often: the From domain has a null MX record
How to fix it if you sent the email
- Add every service that sends as your domain to one SPF record with the SPF generator.
- Check the result with the SPF checker, and set up DKIM and DMARC too.
- If the bounce mentions null MX, send from a domain that can receive email or replace the null MX with real MX records.
If you manage the receiving or sending mail system
- Make sure the envelope sender (Return-Path) domain is covered by SPF, not only the From domain.
Free tool: paste the full bounce into the bounce message decoder to get a plain-English reading of every code in it.
Questions people ask
- What does 550 5.7.27 mean?
- At Gmail, this code means your message failed SPF and Gmail requires bulk senders to pass SPF. Other mail servers use the same code for a different, rarer problem: your From domain publishes a "null MX" record, which says it never receives email.
- Is 550 5.7.27 a hard or soft bounce?
- Blocked. The address is probably fine. The problem is how the mail was sent.
- Should I remove the address after a 5.7.27 bounce?
- No. Fix how the mail is sent; the address itself is probably fine.