How can I access my Office 365 mailbox using IMAP?
You can connect to Office 365 Exchange Online using the following IMAP settings. When connecting, your username is not always your email address. It could end with @somthing.onmicrosoft.com or any other options when it was first setup.
Service Hostname Encryption Authentication Port
Incoming Mail Server (IMAP) outlook.office365.com
SSL Required 993
Outgoing Mail Server (SMTP) smtp.office365.com
TLS Required 587
Server name: outlook.office365.com
Encryption method: SSL
Using IMAP to connect to your Office 365 Exchange Online mailbox synchronizes mail only. Your calendar and contacts can be synced if your email client supports ActiveSync or connecting to an Exchange server.
Please Note: In order to use Office 365 as your SMTP server, you must have an Office 365 mailbox.