Office365 MailProxy 2.0.106

This software is intended for use as a mail proxy between legacy mail clients and Office 365, which requires an OAuth authentication since 2022. The proxy serves transparent in between and handles POP3 and SMTP procotol. The proxy can be used integrated in ET-Connector or standalone.

Setup office 365

The following steps show how to enable an application access through OAuth mechanism in Office 365. The principal is explained at but documentation has some caveats.

Login into Entra Admin Center with administrative right

Goto the organization overview and note the organization-id or tenant-id


Register a new app


Give a useful name, i.e. O3654ET


Note the application-id of the new app!


Create a new secret and note the client secret value, not the client id!

Note: The client secret has an expiration date, take care of this date. If the service cannot login anymore, the server returns an error "unknown user name or bad password"


Add API permission