I noticed that my phone kept failing to log in to the server. Looking at the logs, it seems that I was exceeding the max number of user ip connections limit.
I don’t know what the default is, but in the symbiosis dovecot.conf it said
protocol imap {
…
mail_max_userip_connections = 30
but that isn’t there in the Sympl equivalent.
Putting that line into /etc/dovecot/sympl.d/40-imap-settings/10-plugins has made the problem go away, but presumably it was removed in Sympl for a reason.
What was the reason? Am I going to hit a snag?