When I have been connected to the Internet for a few (undetermined) minutes and then hit the Get Mail button, Claws Mail takes FOREVER to retrieve mail. I often have to disconnect from the Internet and reconnect. Mail fetching is always normal after I have freshly connected to the Internet. No errors are given. I am checking several mailboxes, and I can see them pass thru the status line at the lower left of the CM window. And they hang up on each one...slowly stepping thru them. Its always much quicker to disconnect and reconnect, and then it blasts thru, depending on how much mail, of course. This has occurred in all version of the Windows port I have used. Have been using CM for about a year.
In addition to the delay in fetching mail. Moving mail between folders is also delayed when the Internet connection becomes "stale." There is no other evidence with other programs of having any connection problems whatsoever. I am often actively communicating with websites, both visiting and FTP'ing, etc, and then turn to check mail and....groan. Also, never had this problem with my prior email clients, Thunderbird and Outlook.
Using XP Pro All accounts are setup as IMAP4 (TLS) non-blocking SSL Error occurs wired & wireless, but seems to be less aggravating on my laptop which is usually wireless but sometimes wired. Error occurs at different physical locations: home, work, girlfriend's. However, these all have the same ISP, which is the local small town phone company. Have not tried it with another ISP.
I am having this same issue with 3.7.8 and 3.9.0 connecting IMAP4 to imap-ssl.mail.yahoo.com port 993. Whenever I leave the connection up for over 60 seconds if I then select a different email or IMAP account there is a delay of 59 seconds. Through trial and error I found this was particular to when Claws issue the NOOP to IMAP4 server. If no NOOP is sent then message selection display or different account message display have no delay. As a work-around I've change the configuration>Preferneces>Miscellaneous>Other>Socket I/O timer to 3 seconds from the default of 59, and Claws will restart the IMAP connection within 3 seconds. With the Network Log open the Yahoo servers is sending an error "connection is broken" after a Claws NOOP message to the server and has it restarts the connection. This could be that Yahoo is not complying to the NOOP or the Yahoo servers are dropping connections after being idle for 'x' seconds. Not sure but wanted to post this work-around for others.
The so-called "work-around" given in comment #3, is not a workaround but an option which directly applies to this situation, which is a network timeout.