[Dovecot] painfully slow uploads

I have several mail accounts, but collect all spam e-mail in the spam mailbox on one of them. After switching to dovecot (from imap-uw) I notice a very slow speed of bulk transfers and a very high CPU utilization by the dovecot's imap process during it -- sustained 62% of my server's Pentium2 @266MHz.

Never saw such effects under imap-uw... My client is KMail (despite the awfull quality of its latest release).

Hope, this helps.

Yours,

-mi