Does this happen with RoundCube 3.1?
Yes this is happening to 3.1 too.
[01-Dec-2009 12:30:08 +0200]: IMAP Error: Empty startup greeting (localhost:143) (GET /?_task=mail&_action=check-recent&_t=1259663498990&_list=1&_quota=1&_remote=1&_=1259663499020&_unlock=1)
[01-Dec-2009 12:30:08 +0200]: IMAP Error: Empty startup greeting (localhost:143) (GET /?_task=mail&_action=check-recent&_t=1259663398386&_remote=1&_=1259663398386&_unlock=1)
[01-Dec-2009 12:30:08 +0200]: IMAP Error: Empty startup greeting (localhost:143) (GET /?_task=mail&_action=check-recent&_t=1259663395754&_list=1&_quota=1&_remote=1&_=1259663395754&_unlock=1)
[01-Dec-2009 12:30:08 +0200]: IMAP Error: Empty startup greeting (localhost:143) (GET /?_task=mail&_action=check-recent&_t=1259663373421&_list=1&_quota=1&_remote=1&_=1259663373437&_unlock=1)
[01-Dec-2009 12:30:09 +0200]: IMAP Error: Empty startup greeting (localhost:143) (POST /?_task=&_action=login)
[01-Dec-2009 12:30:11 +0200]: IMAP Error: Empty startup greeting (localhost:143) (GET /?_task=mail&_action=check-recent&_t=1259663406958&_remote=1&_=1259663406963&_unlock=1)
[01-Dec-2009 12:30:11 +0200]: IMAP Error: Empty startup greeting (localhost:143) (GET /?_task=mail&_action=check-recent&_t=1259663403063&_remote=1&_=1259663403063&_unlock=1)
[01-Dec-2009 12:30:12 +0200]: IMAP Error: Empty startup greeting (localhost:143) (POST /?_task=&_action=login)
[01-Dec-2009 12:30:12 +0200]: IMAP Error: Empty startup greeting (localhost:143) (POST /?_task=&_action=login)
[01-Dec-2009 12:30:12 +0200]: IMAP Error: Empty startup greeting (localhost:143) (POST /?_task=&_action=login)
[01-Dec-2009 12:30:15 +0200]: IMAP Error: Empty startup greeting (localhost:143) (POST /?_task=&_action=login)
[01-Dec-2009 12:30:16 +0200]: IMAP Error: Empty startup greeting (localhost:143) (POST /?_task=&_action=login)
[01-Dec-2009 12:30:17 +0200]: IMAP Error: Empty startup greeting (localhost:143) (POST /?_task=&_action=login)
[01-Dec-2009 12:30:19 +0200]: IMAP Error: Empty startup greeting (localhost:143) (POST /?_task=&_action=login)
any idea on this?