Please note that Zammad 3.1 is no longer up to date, you might want to try out Zammad 3.2 (read this before: Zammad 3.2 is available )
Also, most of your issues sound like performance issues.
Please provide the following information:
* Number of CPU cores available to Zammad
* Used CPU (e.g. Intel Xeon xyz)
* Available memory for for Zammad
* Number of Tickets (rails r 'p Ticket.count')
* Number of Users (rails r 'p User.count')
* Number of Agents (concurrent)
* Number of overviews (rails r 'p Overview.count')
Above covers at least issue 1 and 3.
Error 3
By default postgresql allows a maximum of 100 connections. This is usually fine, your environment however seems to have a load of workload, you may want to increase the number to 250. This should be fine.
I can not reproduce issue 4 - haven’t seen that in a while.
Issue 5 can be ignored and is just a warning for signature recognition. It doesn’t break anything. Promise!
Another interesting question for your mail issue would be, if it’s always the same type of mail that fails and whats inside. Some specific mails can cause issues. But as you can import them later, it’s most likely just a performance issue.