Sorry to awaken such an old thread, but I'm also still having these slow responses time.
I've done reasonable troubleshooting and every point I get to leads to the IMAP process that takes unusually long to get the data from the mailbox.
We've got one host that RC connects to which points to 4 mail servers running in a cluster with Courier-IMAP. I've setup 3 different versions of RC on 3 different servers pointing to our mail host as well as tests servers and get the exact same problem.
While doing a top on the mail server that RC is connecting to, I notice that the IMAP process is using quite a lot of resources when you login to RC. Is this normal? I've also tried 0.6, but found that even this version is doing the same.
I also have tried using IMAP Proxy and even the tweaks in the RC help sections and these don't work either. I've also set the connection to be standard plain text authentication without TLS and SSL to speed up the connection so as no encryption is being used.
I'd appreciate it if someone has found a solution to this and will share their fix please.
Cheers.