Thunderbird Finally Supports Exchange — But Open Standards Still Win
Thunderbird now includes native Microsoft Exchange support, but many of the historical issues with IMAP, SMTP, and Microsoft’s proprietary protocols remain relevant. This article explains what changed and why open standards still matter.
By. Jacob
Edited: 2025-11-30 12:42
I recently tried to set up e-mail in Thunderbird for Microsoft Exchange. Back then, I gave up — and for good reason. At the time, Thunderbird did not support Exchange natively, and the only way in was through IMAP/SMTP or a paid plugin.
Update (30 November 2025): Thunderbird now includes native Microsoft Exchange support. The issues described in this article reflect how things worked before this update, when standard protocols or paid extensions were the only ways to connect.
Source: Thunderbird Adds Native Microsoft Exchange Email Support — blog.thunderbird.net
The official documentation did not explain how to use POP3 or IMAP protocols properly, and as usual, Microsoft support forums did not provide any meaningful help.
Some discussions suggested that the organization admin might have to enable IMAP and SMTP before it would work. But after logging in to my webmail account, I was unable to find anything confirming whether I could connect using standardized protocols. A simple list of enabled protocols would have helped immensely.
I did manage to connect to the IMAP server using SSL/TLS with OAuth2, but for some reason the SMTP server refused to authenticate or send e-mail — while falsely claiming the login details were wrong.
Also note that Microsoft Exchange does not support basic authentication with IMAP, POP3 or SMTP anymore. Instead, OAuth2 is required, and many e-mail clients at the time did not support it properly.
The correct IMAP settings for Microsoft Exchange are as follows:
Server name: outlook.office365.com
Port: 993
Encryption method: SSL/TLS
And if you preferred POP3:
Server name: outlook.office365.com
Port: 995
Encryption method: SSL/TLS
Both required OAuth2 authentication.
The SMTP settings listed by Microsoft were:
Server name: smtp.office365.com
Port: 587
Encryption method: STARTTLS
But at the time, SMTP simply refused to function correctly, regardless of the authentication method chosen.
Note. Some organizations use their own hostnames (such as mail.company.com or imap.company.com), so you may need to use the server name provided by your administrator instead.
Microsoft Exchange support on Linux
Before the recent Thunderbird update, there was no native Exchange support on Linux. The only viable alternative to IMAP was the Owl extension for Thunderbird — but since it was not free, it was never an acceptable solution. Paying for such basic functionality felt unreasonable.
Evolution did not work for me, and KMail was broken due to an Akonadi issue. For a long time, Thunderbird was the only free and open source client left, but it lacked native Exchange support — until very recently.
E-mail is such a basic technology that paying a subscription for access to a proprietary protocol ecosystem never made sense to me. The Owl extension was also massively overpriced at 10 EUR per year. If it were a one-time fee, maybe — but I refuse to pay recurring subscriptions for essential software.
The real question remains: why not stick with standardized protocols? IMAP and POP are broadly supported, work everywhere, and do not lock users into a single vendor’s ecosystem.
Please do not use Microsoft Exchange in your company unless you enable support for IMAP and SMTP. Even though Thunderbird now supports Exchange directly, standardized protocols are still the most interoperable solution.
Microsoft needs to support Linux
Back when I was still using Windows, I stopped relying on Microsoft's e-mail clients because they proved unreliable over time. Microsoft frequently discontinues older clients and replaces them with worse alternatives. Migrating between them is risky, since exporting and importing mail is unnecessarily complicated.
Support for Outlook Express was discontinued, then Windows Live Mail was abandoned and replaced with a worse built-in mail app. Naturally, many users escaped to Thunderbird.
Much like web browsers benefited from going open source, e-mail clients clearly benefit from it as well. I no longer trust non–open-source mail clients; if a company stops maintaining its product, users are stranded. E-mail is simply too essential for that risk.
Microsoft Exchange has an overly aggressive anti-spam
This is a separate issue, but still a significant downside of using Microsoft Exchange.
I tried sending an e-mail from my own server to my Exchange-hosted account, and it never appeared in my Inbox. My client would not download it, and Exchange silently discarded it without notifying me.
This makes me fear I might miss important e-mail.
That is unacceptable for a service marketed as “professional”. Worse yet, I found no option to disable the broken anti-spam filter. It appears to be something only the organization’s admin can change — if it is even possible at all.
Ideally, individual users should be able to disable the spam filter entirely on their accounts.
Tell us what you think:
Microsoft has deprecated the older protocols for security reasons. 365 admins can enable Oauth2, if they want to. Instructions for this on Microsoft and third-party sites.
Microsoft cannot “deprecate” IMAP or POP3 — they don’t own them.
These are open IETF standards, and only the IETF can revise or deprecate them. Microsoft can only disable support for IMAP/POP3 on their own services, which is a mistake, because Exchange itself is not an open protocol.
Microsoft has zero authority over the standards, aside from their own proprietary Exchange protocols — and those are opaque, undocumented, and potentially full of issues for exactly that reason. IMAP and POP3 remain open, transparent, and widely implemented across the entire Internet.