Microsoft has announced end of life support for basic authentication for office 365 - the 13th October 2020.
Will the AE.Net.Mail libaray (currently version 1.7.10.0) still be usable to connect after this date using
var client = new ImapClient(host, username, password, AuthMethods.Login, port, true);
No, AE.Net.Mail will not work anymore for Office365 once Microsoft ends support for basic authentication.
You'll need an IMAP library that supports the XOAUTH2 SASL mechanism.
Update: I've had several people ask me how to obtain the proper OAuth2 access-token credentials via Microsoft Graph for use with MailKit, so I've reached out to the Office365 development team in order to try and get that information. Once I've got that info, I'll write up a HOWTO document and include it with MailKit.