Mail.app has been reaching new levels of cantankerous behaviour recently. Although the 10.3.9 update seems to have cured the majority of “crash on scroll” problems I was having, it has taken to pounding my mail server into the ground at every opportunity.
Each time I wake up the powerbook or start Mail, it will cheerfully open well upwards of 100 IMAP connections. This is incredibly bad behaviour. My laptop grinds to a halt, the server cries out in pain, and then either Mail will hang or the IMAPD on the server quits in protest.
It turns out the culprit was the “Automatically synchronize changed mailboxes” option in the advanced preferences for my main account. I had this selected, because I have a large number of folders and I don’t like the sluggish response time when Mail has to synchronise when you switch between them. But I dislike Mail killing my server more, so for now I’ll live with it.
I’m going to study Thunderbird’s preferences now, to see if I can convert my Mail.app filtering rules to an appropriate Thunderbird format.