I just migrated my MIAB to v.41 and Ubuntu 18.04. Since being on the new setup, my incoming emails are taking about 10 minutes to appear in the mailboxes. Previously I would get incoming messages in less than 30 seconds.
I sent a few test emails from Mandril’s SMTP server so I could see the sending logs, and they show as send and received long before I actually get the message.
Any idea how I can speed up the incoming mail availability process?