SMTP server slow transaction time connection issue


Recently connecting to the SMTP server has got very slow and sometime it won’t connect at all.

From the mail log of the email client it appears the problem may lie with the time it takes to authenticate.

WROTE Jul 12 15:14:29.377 [kCFStreamSocketSecurityLevelTLSv1_2] – – port:587 – socket:0x6000006a1b60 – thread:0x60400026c600
AUTH PLAIN (*** 72 bytes hidden ***)

READ Jul 12 15:15:49.663 [kCFStreamSocketSecurityLevelTLSv1_2] – – port:587 – socket:0x6000006a1b60 – thread:0x60400026c600
235 2.7.0 Authentication successful

Also testing via MXToolBox the transaction time is slow.

However what I can’t understand is that this doesn’t happen all the time and no changes were made to Postfix configuration.

The amount of mail which is usually in the mail queue is tiny i.e. under 10

Any ideas what to look for / check etc I would be most grateful.

Centos 6
Postfix 2.6.6

Check DNS resolution on the host itself and make sure that if you’re listening on IPv6 you actually have an IPv6 configuration that works and is fast (and matching DNS for IPv6). Slow email is nearly always DNS-related.

Hi Joe

Thanks for getting back to me. I think I may have sorted it.

In I changed tls_preempt_cipherlist=no to tls_preempt_cipherlist=yes

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