The IMAP standard is known to be vague in places and different servers implement it in different ways. Some server also have long standing bugs that a client ha

The IMAP standard is known to be vague in places and different servers implement it in different ways. Some server also have long standing bugs that a client has to deal with gracefully. And of course you still have to implement SMTP, POP3 and possible a bunch of different protocols for searching, address book and calendar synchronization.