Hello @allypitman ,
Thank you for your message.
Post SMTP shows the email as “Sent Successfully” because your mail service accepted the message without any errors. However, Yahoo performed its own checks afterward and bounced the email, which happens outside Post SMTP’s control.
A bounce from Yahoo typically indicates issues such as:
- SPF/DKIM/DMARC not fully aligned
- The “From Email” not matching the authenticated domain
- Yahoo filtering or blocking the sending IP/domain
To identify the exact cause, please share the bounce message you received. That will tell us precisely why Yahoo rejected it and how to fix it.
Happy to help you resolve this.
Support Team – WP Experts
the bounce back email had this message (I’ve taken out the persons email:
the email address
host smtp-relay-float.mail.stackcp.net [10.4.0.246]
SMTP error from remote mail server after RCPT TO:<email address>:
550-“Please enable DKIM for your domain. Yahoo requires all senders to
550 authenticate with DKIM – https://senders.yahooinc.com/best-practices/“
Reporting-MTA: dns; smtp1.lhr.stackcp.net
Action: failed
Final-Recipient: rfc822; the email address
Status: 5.0.0
Remote-MTA: dns; smtp-relay-float.mail.stackcp.net
Diagnostic-Code: smtp; 550-“Please enable DKIM for your domain. Yahoo requires all senders to
550 authenticate with DKIM – https://senders.yahooinc.com/best-practices/“
But further emails sent, have been received by the intended recipient
Hello @allypitman ,
Thank you for sharing the bounce details.
Yahoo rejected that specific message because your domain did not have DKIM enabled or passing at the time the email was sent:
550: “Please enable DKIM for your domain. Yahoo requires all senders to authenticate with DKIM.”
This means the receiving server checked your DKIM signature and didn’t find a valid one, so it blocked the message.
The fact that later emails were delivered successfully indicates that:
- DKIM was enabled or fixed shortly after
or
- Your mail provider began signing messages correctly again
So the issue was most likely temporary, either DNS propagation or the server not signing that particular message at the time it was sent.
If everything is working now, no further action is needed.
Warm regards,
Support Team – WP Experts
