Exim4 sends messages after a long delay

Community Support Mail
1

I noticed that every once in a while, Exim4 sends messages after a long delay, ~15 min or so. I know it’s not the rate limit, because when that one is exceeded, Exim gives a rate limit error. We use emails for signups, so user onboarding fails when that happens.

Does anyone know if there is throttling or some other setting for Exim that may be causing this delay?

2

could be greylistening, have a look at the exim mainlog.

3

I checked. There is no entry in /var/log/exim4/mainlog for the recipient email address at all. Then, it appears when the email is actually sent about 15 min later without any errors with C="250 2.0.0 OK.