Microsoft 365 / basic auth deprecated / service mailboxes for apps+devices

I am hoping someone can help me make sense of the whole Microsoft deprecating basic auth with 365, and how service mailboxes for apps+devices fit in at all.

Basically, our parent company turned off basic auth for the entire tenant whenever the date was that Microsoft planned for that to be deprecated. Back then, I only had a minimal need for a few service mailboxes, and could get away with just a quick and dirty on-prem SMTP relay. Now I am anticipating a greater need for such service mailboxes, or at the very least the ability for apps/devices to send email. It would not make sense to me that Microsoft would deprecate basic auth /and/ completely cut off access to apps+devices… it seems far more likely that I have simply missed something here, and maybe waited too long and forgot exactly what I needed to search for. Can anyone help?

Google has done the same, my solution is to use tools like this:


We have Mimecast and have been using that where we need SMTP relays for a couple of years. We still have a couple of on prem SMTP relays that now point to Mimecast for things like printers.

We have a couple of helpdesk systems that pull tickets from a licensed 365 mailbox using IMAP. This depends on your software vendor to support modern auth in their app.

If you have software which doesn’t support modern auth, there are some open source authentication proxies intended for this purpose but I haven’t used these and I cant make any recommendations - This is one example I came across though.

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Awesome, thank you both!

The quick and dirty SMTP relay I have set up is just whatever is in IIS on the on-prem Exchange server, but it was never meant to be anything more than a quick solution. Plus, I’m still stuck behind Microsoft’s policies there because it can only send to internal domains.

I actually started using DuoCircle yesterday thanks to Tom’s recommendation, but Mimecast could probably work just as well. Simplicity is key here, and DuoCircle absolutely nails that. Thank you both!