I received a few complaints from different people, that sending of email messages is really slow. This didn’t make any sense, because no modifications were made on the server.
After an hour, I found that this was caused by Exim setting “Delay SMTP Transaction”. Quoting cPanel: The SMTP receiver will wait a few additional seconds for a connection when it detects spam messages in order to reduce inbound spam.
So it’s another weapon to fight spam mail, but it makes sending slower.
You can disable this feature in Exim Configuration Manager -> ACL Options -> Introduce a delay into the SMTP transaction for unknown hosts and messages detected as spam.
When disabled, your emails should be fast again.