Outlook cannot send when connected to IMAP, but it can send mail if I connect it to POP3
Depending on the client, sending mail might fail for example if IMAP fails to save a copy to the Sent folder. This part has nothing do with SMTP, as SMTP isn't typically used for sending copies to oneself (and if it was, they would probably appear in Inbox). Some clients may also send first and save afterwards, so you may even end up sending mail without knowing it was delivered.