Email delivery after SMTP basic auth ends in late 2026

For devices or applications that don't support OAuth 2.0, you will need some sort of SMTP relay. While I haven't used it in prod yet, I've been testing out https://github.com/JustinIven/smtp-oauth-relay This runs in a container, and acts as a compatibility layer for applications that don't support OAuth 2.0 natively, using `tenant_id@client_id` as the username and the app's client secret for the password. This means that you could conceivably use a single instance as a relay for multiple clients. The big catch I've found is that some older or simpler devices may not be able to handle the long strings needed for either the username or password. The most future-proof solution, as you've hopefully been trying to convince your clients, is obviously to replace any devices or applications that can't be updated to use OAuth 2.0. This is *not* a surprise, and vendors have had years to prepare and roll out updates. And as a reminder, disable Direct Send as soon as possible, as having that enabled allows for spoofed phishing emails "from" your users sent by virtually any country with no verification. https://techcommunity.microsoft.com/blog/exchange/introducing-more-control-over-direct-send-in-exchange-online/4408790