Microsoft OAuth

Refresh Tokens

When using Microsoft OAuth with SMTP or IMAP connections, refresh tokens expire after 90 days. Every time you use the refresh token though, you are issued a new one that won't expire for another 90 days, so... as long as we are always saving the new refresh token we get back in the response, the connections should only expire if an email is not sent for 90 days with that setting. 

If we were to add a background process that periodically refreshed Microsoft OAuth connections, even if an email wasn't sent for 90 days, the connection would not expire.

see Microsoft's documentation here