I have an IMAP/POP3/Webmail server with Dovecot1 2.2.10 with a MySQL backend located on another server. The server runs with default configuration.
... driver = mysql default_pass_scheme = plain ...
My problem is that sometimes when it gets overloaded it start refusing authentication (aka it says bad password) of the clients. It does this for all different types of clients (pop3,imap,webmail) so this must be an authentication backend related issue
My first thought is that there aren't enough dovecot authentication processes running.
What can I tune and in what order for this system to be able to handle more client authentication requests simoulteanously?
My MySQL server is not overloaded, it's a quadcore machine with an average 25% CPU usage during the day.
The CPU usage of the mailserver itself spikes up during this period. Memory usage remains normal.
This is a production system so all I can do is adjust some variables which surely won't break it.