Comment How about implementing correct IMAP support? (Score 1) 49
When it comes to IMAP - a well-documented and widely implemented e-mail protocol - Microsoft takes a "not invented here" attitude to it and has a disgracefully half-baked IMAP implementation of it in Outlook. Pretty well every popular non-Outlook mail client out there implements IMAP correctly, but a trillion dollar company called Microsoft apparently can't.
My biggest grievances are that it often won't pick up changes to your IMAP inbox automatically and it doesn't implement the IMAP delete properly either (leading to mail not being deleted on the server while Outlook only deletes its local copy - not good if you have a mail server quota [another thing that Outlook doesn't query by IMAP either]).