Comment 130 for bug 275471

TB never marks attachments with content disposition inline when sending, I don't think, so a RAR archive sent from TB won't be fetched when you click on a message, independent of the display attachments inline setting. I think most peoples' complaint has to do with image attachments, which we do know how to display inline. Turning off view | display attachments inline *should* make it so we don't try to fetch those images when you click on a message.

The offine auto sync issue is somewhat different. Autosync tries not to download large messages (> 50K) unless you're idle. But it has an aggressive definition of idle (no keyboard activity for 10 seconds, or an other window is in front). We could try to fetch large messages for offline use using chunking, to allow the process to be interrupted by the user, but it can slow down download drastically, which is extra bad for large messages. We deliberately don't cache partial messages in the offline store, so that we don't accidentally think we have the complete message when it's just partial.

You may have also run into a bug where we go idle on startup, if startup takes too long.