For me Mail.app isn't able to connect to my mail server which runs courier IMAP server Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. * OK [CAPABILITY IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT QUOTA IDLE STARTTLS] Courier-IMAP ready. Copyright 1998-2003 Double Precision, Inc. See COPYING for distribution information.