PMDF System Manager's Guide

The first thing to check is whether the clients are timing out when they try to connect, or when they try to send mail. If the trouble is when users try to connect to read messages, then you need to investigate the POP or IMAP server, according to which sort of client is having difficulties. But note that POP and IMAP clients send mail out using SMTP and the SMTP port, so if the trouble is when users try to connect to send messages, then you need to investigate the SMTP server.

The POP, IMAP, and SMTP servers are controlled by the PMDF Dispatcher. For the server in question, check the Dispatcher configuration for the maximum number of servers allowed for that service (MAX_PROCS), and the maximum number of connections each individual server can handle (MAX_CONNECTIONS). Then check how many such server processes are actually running. If you have more than MAX_PROCS*MAX_CONNECTIONS users trying to connect simultaneously, then you can want to increase the total number of servers allowed, or perhaps the number of connections each server can handle---though note that allowing too many connections per server tends to degrade the performance for each particular connection.

Additionally, general system resource and quota problems will of course impact the servers. See, for instance, Section 33.4.4.