The Thunderbird blog post also mentions they are looking to support the Microsoft Graph.

More limiting is that the current release doesn't support custom Office365 tenant IDs. So basically, unless you are using outlook.com this won't currently work yet. I'm lucky that my org hasn't disabled SMTP and IMAP, but it's been so slow lately...

Someone might be wondering why someone might have different URLs. One example is anyone under sovereign clouds (eg. GCC, GCC-High) which use different URLs (and TLDs) across the board (eg outlook.office365.us)

> it's using EWS (Exchange Web Services) which is being removed in October 2026 for Office36

This is Microsoft we're talking about here, so if its slated for removal in Oct '26, it will be put into LTS, and finally 'retired' (but operational) _starting_ around 2031.

Microsoft swears it's happening: https://techcommunity.microsoft.com/blog/exchange/retirement...

Take the blog article for what you will. I have noticed in Office365, they tend to be less backward compatible than you would expect from Microsoft.

  > Microsoft swears it's happening

And when has that ever meant it comes without delay?

Up to you if you believe Microsoft or not. I don't really care, I haven't messed with 365 outside being end user in years.

to be fair with you, EWS has been deprecated since I think 2014, so we're already in the "pushed" window.

As an on-prem admin, I am blown away that there's 30-40 changes to 365 monthly, often including at least two or three feature deprecations. It seems like building a building on top of quicksand.

The have been keeping to the timeline when it comes to other recent Exchange Online removals (certain auth roles).

The new Microsoft is unfortunately not like the old one.

How do you know Thunderbird is using EWS, not MAPI? MAPI is not going away any time soon.

Read the docs? https://blog.thunderbird.net/2025/11/thunderbird-adds-native...

Yikes, thanks. Enjoy this feature while it lasts, I guess. EWS is getting nuked.

Read the article?

As you imply though, it remains for on-premise. They're working on msgraph as well luckily.

I updated my post to reflect yes, this is Office365 only. On premise will continue to support EWS. Depending on where you are, Exchange on premise is becoming extinct.

You'll recall how horrendous on prem Exchange updates could be. Surely the sheer amount of time involved was a nudge and nothing technical?

My tiny company had an on prem Exchange, migrated from GroupWise, and is now cloudy. I did all the migrations myself.

I have left things with our MX records pointing to on prem (Exim + rspamd + stuff) and relaying to MS 365 and a few IMAP daemons. If MS take the piss with licensing costs, I'll simply relay elsewhere and drop them.

Then I'll migrate my customers away. It'll take a while but it is not insurmountable.

FWIW: I use Evolution on my Kubuntu based gear to access M365 email. Wifey rocks Arch and I've deployed Evo on KDE there too.