Authentication failed

Since last week, we no longer receive emails on the ticket server. We use Microsoft Mail Server Office365. We use an Reverse proxy server.

Error:
upstream prematurely closed connection while reading response header from upstream, client: 10.56.65.51, server: zammad.g-i-m.com, request: “GET /ws HTTP/1.0”, upstream: “http://127.0.0.1:6042/ws”, host: “zammad.g-i-m.com

Expected behavior:

Actual behavior:

Steps to reproduce the behavior:

Did you setup the account on the “Microsoft 365” menu entry? If not, maybe you run into a deactivated* basic auth, and you have to use the modern auth from the MS365-menu.

*MS randomly deactivate the basic auth from some tenants before the EOL in Oct. 22 is reached.

BTW: You can request to re-enable basic auth and extend the deadline until 1.1.2023 if you need more time to make the switch.