[jff]

The lack of proper multithreading has bit me many times when I try to use Emacs as an email client--start talking to the IMAP server, and your whole Emacs process takes a break. Can't edit anything, we're stuck until it either finishes or you hit C-g.

[jrockway]

I use IMAP over SSL with Gnus, and the actual talking-to-the-network is asynchronous (handled by another UNIX process). The slow part is generating the summary buffer on large groups.

(BTW, if you use IMAP with Gnus, I highly recommend using a local IMAP server instead. You can sync to your remote IMAP server with offlineimap. This speeds up Gnus enormously for me; reading my Maildir directly from Gnus is too slow to be usable, but reading it through a local IMAP server makes reading my inbox instantaneous.)

[drewr]

I run a dedicate instance for Gnus for exactly that reason. Has the added benefit of keeping me from being distracted by a simple (Emacs) window change when I'm focused in my other instances.