source: http://www.securityfocus.com/bid/31997/info

Dovecot is prone to a remote denial-of-service vulnerability because it fails to handle certain specially crafted email headers.

An attacker can exploit this issue to prevent recipients from accessing their mailboxes.

For an exploit to succeed, the IMAP client connecting to Dovecot must use the FETCH ENVELOPE command.

The issue affects Dovecot 1.1.4 and 1.1.5. 

The following invalid message address header is sufficient to trigger this issue:

"From: (" 