Relay access denied is a very common email error, so I wasn’t surprised when I received one while setting up email for a new domain, which I used VestaCP to set up. To improve email delivery, I enabled DKIM.
Unfortunately, I did not complete the process before sending the first test email to an account under the new domain. So right after the email was sent, I received the Undelivered Mail Returned to Sender email, a partial content of which is shown below:
# The mail system <firstname.lastname@example.org>: host eforward2.registrar-servers.com[162.xxx.xxx.62] said: 550 5.7.1 <email@example.com>: Relay access denied (in reply to RCPT TO command) #
A little bit of digging showed that though DKIM was enabled, I forgot to set up a TXT record using the DKIM public key for the domain. So I took care of that, sent another test email, and that was it. A simple error can cause some major headache, so next time you’re setting up DKIM and are unable to send or receive email, check that you’ve created a TXT record for the domain.