Email Delivery Delays

Issues related to applications and software problems
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nguyentuantuan16
Posts: 1
Joined: 2021/10/20 02:33:22

Email Delivery Delays

Post by nguyentuantuan16 » 2021/10/20 02:38:00

CentOS 7, Postfix, Dovecot. Fully updated.

For some days ago I notice some emails from our email server are not being received for several hours. The effect seems random. Some emails punch through immediately, other emails take several hours to be received.

I don't see anything obvious in the logs but this could be me not seeing the tip of my nose. Looking for suggestions and ideas.

We use an external spam filter service. I don't know if that is playing a role.

There was the recent mass CentOS 7.9 patches. I updated the server Nov. 17. There was an updated dovecot package. I don't know if that plays a role. I did not record when the delays started and while coincidence does not mean causation, the latest updates might be related.

Thank you!

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TrevorH
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Joined: 2009/09/24 10:40:56
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Re: Email Delivery Delays

Post by TrevorH » 2021/10/20 17:09:51

If this is for email outbound from your machine then dovecot does not come into the equation. Check your /var/log/maillog and see what it says about some of these delayed emails. If the status on them says 'sent' and the receiving MTA is your spam filter service then it's likely to be their side that is the problem. It could also be that the machine you are sending from and the domain you use are not set up correctly for anti-SPAM measures like SPF and/or DMARC. Many recipients will 'greylist' mails that are not set up to use SPF/DMARC and that will incur a delay.
The future appears to be RHEL or Debian. I think I'm going Debian.
Info for USB installs on http://wiki.centos.org/HowTos/InstallFromUSBkey
CentOS 5 and 6 are deadest, do not use them.
Use the FAQ Luke

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