Spammers. Spam email now accounts for how much traffic on email servers.
So with the spammers blasting away at the servers and no real reason to increase server power everyone just lets it timeout and retry.
No one plans to fix this. Very few will tell you the truth.
i am using windows 7 with thunderbird as an email client. (also use outlook 2010 on another win 7 machine) and email settings for an IMAP/SMTP email server are correct according to ISP. everything runs fine and then server timeouts occur apparently random.