How to solve: Undelivered Mail Returned to Sender

OS type and version Ubuntu Linux 20.04.5
Webmin version 2.013
Usermin version 1.861

Hi Dear,
I receive mail easily but when I send an email to my id example@gmail(.)com then it sends the following message to example@domain.tld:

This is the mail system at host host.domain.tld

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<[example @gmail com](mailto:example @gmail com)>: connect to[2607:f8b0:4001:c56::1a]:25: Network is

Reporting-MTA: dns; host.domain.tld
X-Postfix-Queue-ID: CF1A87E3EC
X-Postfix-Sender: rfc822; [name @domain.tld](mailto:name @domain.tld)
Arrival-Date: Wed, 8 Feb 2023 20:51:17 +0000 (UTC)

Final-Recipient: rfc822; [example @gmail com](mailto:example @gmail com)
Original-Recipient: rfc822;[example @gmail com](mailto:example @gmail com)
Action: failed
Status: 4.4.1
Diagnostic-Code: X-Postfix; connect to[2607:f8b0:4001:c56::1a]:25: Network is

Pls, Check my issue. How can I resolve this issue?
Thanks in advance.

Note: I added space between “@” and COM.


Contact Google… the error is pretty clear “Network unreachable”. Likely a temporary issue, but if it persists only Google can fix.

If Google is not offline, you could check if your vps service provider has blocked port 25 of your vps.

This would prevent you from sending email to your Gmail account or to any other email address on the internet.

either what @calport said (port 25 blocked), or your ipv6 network settings need fixing.
(google is not offline.)

It looks like you’re trying to send over IPv6 but that your IPv6 connectivity isn’t set up properly

What you could try is to edit /etc/postfix/ :

  • Change inet_protocols = all to inet_protocols = ipv4
  • Then: sudo service postfix restart

(This assumes that your mail server is otherwise set up correctly)

1 Like

This error typically indicates a problem on the receiving server. Try these fixes: Make sure the recipient address is valid. Reduce the number of recipients in the message. If you received this error when sending a message using Outlook or another email app, try using to send the message instead

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