smtp – Configure Postfix to use Mailgun – Error sending the same domain

We use Mailgun SMTP to send emails. In the main.cf of postfix we added the usual relay / sasl settings:

# Amavisd + SpamAssassin + ClamAV
#
content_filter = smtp-amavis:[127.0.0.1]:10024

# Concurrency per recipient limit.
smtp-amavis_destination_recipient_limit = 1

relayhost = [smtp.mailgun.org]:587

smtp_tls_security_level = encrypt
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = static:login@domain.com:password
smtp_sasl_security_options = noanonymous

Works fine and email deliveries are properly logged under Mailgun.

The problem
If we send an email within our domain, Mailgun will not be triggered. Medium: if JohnDoe @abcDomain.com sends an email to JaneDoe @abcDomainwill be delivered via Postfix. If JohnDoe @abcDomain.com sends an email to JohnDoe @xyzDomain.com, which is part of another domain, is delivered and logged via Mailgun smtp.

We have no explanation for this behavior. Maybe we missed something?

Thank you for every hint

Intermittent Bounces – Exim / WHM on GCP to Mailgun

When working on a Google Cloud Platform instance, I set everything up with WHM / cPanel and sent emails to Mailgun via Exim. Everything worked fine until I started sending some of my heaviest email with clients. Now I'm in the middle of a blame game between cPanel and Mailgun support. Both say the problem is the result of the other.

At first, I couldn't replicate the problem myself. After a few days of trying to replicate the problem, it occurred several times in a row. Below is an edited version of the returned email. dest@domain.tld = the email address to which the email should be sent. Hostname = the first part of the server hostname, not the full hostname. For example hostname.domain.tld it is only the first part.

Code:

host smtp.mailgun.org [52.24.250.149]
SMTP error from remote mail server after RCPT TO::
550 5.7.1 Relaying denied
Reporting-MTA: dns; hostname

Action: failed
Final-Recipient: rfc822;dest@domain.tld
Status: 5.0.0
Remote-MTA: dns; smtp.mailgun.org
Diagnostic-Code: smtp; 550 5.7.1 Relaying denied

At this point, both cPanel support and Mailgun support agree that the bounce is the result of an authentication error. However, since cPanel claims that authentication works most of the time, it must be a bug on the Mailgun side. Using the same logic, Mailgun support says that it is a problem on the server side.

What we have done so far:

  • Switched from hosts_try_auth to hosts_require_auth
  • Enabled detailed logging of Exim and Dovecot
  • The port number has been changed from 2525 to 587
  • Activated SRS transmitter rewriting scheme
  • Reapply the hostname.domain.tld server and apply the workaround from https://docs.cpanel.net/knowledge-ba…name-solution/.

The cPanel support informs me that logs from Mailgun's side of the rejection are required. However, Mailgun does not log authentication attempts.

Have you ever received an answer from Mailgun Support?

Have you ever received an answer from Mailgun Support? | Web Hosting Talk

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  1. * Have you ever received an answer from Mailgun Support?

    We decided to test Mailgun because we had problems with the delivery
    With Sparkpost, however, it seems that some of their IPs are also banned in Hotmail.
    So I sent you a message from the contact form on their website
    I have never received an answer
    a reliable alternative.


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