Thunderbird Outlook outgoing connection issue

Question

Thunderbird Outlook outgoing connection issue

philip lightfoot 0

Thunderbird outlook connection issue.

When I set up the SMTP outgoing server in thunderbird you can test the connection.. I get a test certificate from microsoft but when I try to send an email the connection fails.

This is the final part of the test certificate.

Thunderbird has been uninstalled and reinstalled many times to try to resolve the issue . Saved passwords deleted etc. Various config settings in config editor checked etc. All outgoing server settings are correct o2auth etc.

Thanks

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2 answers

Your answer

Answer 1

@philip lightfoot said

When I set up the SMTP outgoing server in thunderbird

I recently setup an Free/Personal outlook.com account in TBird using OAuth. And at no point did I have to specify the SMTP settings. TBird's auto discovery did everything for me. The only snag was I had to allow IMAP access to my Outlook.com account (see below).

User's image

To enable IMAP access to your outlook.com account:

Logon to your outlook.com account at https://outlook.cloud.microsoft/
File -> Settings -> Email -> Forwarding and IMAP
If there is a [Sign in] button, click it and Sign-In (again)
( o) Let devices and apps use IMAP

Answer 2

Lucus-V 10,425 Microsoft External Staff Moderator

Hi philip lightfoot,

Do you have the latest version of Thunderbird?

Regarding the information from Microsoft OAuth Authentication and Thunderbird in 2026, they suggested that customers should update to the latest release to be compatible with improved Microsoft standard.

Disclaimer: This is a non-Microsoft website. The page appears to be providing accurate and safe information. Watch out for ads on the site that may advertise products frequently classified as PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.

If the problem persists after installing the latest version, please feel free to let me know.

philip lightfoot 0 Reputation points

2026-07-18T07:16:18.4266667+00:00

Thank you for your reply.

Yes I have the latest version of thunderbird ie 152.0.01 on both my desktop and laptop

Desktop has updated Windows 11 25H2 and laptop Windows 10 newly installed about 1 month ago.

The same problem on each.

If after the initial failure I select the try new password option this box opens but it is blank.

https://account.live.com/App/Confirm?mkt=EN-US&uiflavor=host&id=292841&client_id=0000000040C8F39E&ru=https://login.live.com/oauth20_authoriz

Above this is the thunderbird logo and words "enter credentials in philip.lig....outlook.com on smtp-mail.outlook.com

Sometimes I get an additional box from Microsoft within the blank box saying, " Are you trying to log into thunderbird. Only continue if you downloaded the app from a store or website you trust. The desktop version is from Mozilla . The laptop version is from Microsoft store.

If I type the above address into my browser. Microsoft says this site is temporarily unavailable due to maintenance
philip lightfoot 0 Reputation points

2026-07-19T14:09:56.1266667+00:00

Thank you for your help.

Yes all that is no problem but when I come to use the outlook account in thunderbird to send an email the connection fails followed by the message, "Sending of the message failed.

Unable to authenticate to Outgoing server (SMTP) . Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'." which I have many times together with uninstalling thunderbird and reinstalling many times.

I have also removed saved passwords and re-entered when prompted when accessing the accounts.

When the connection fails there is the option to"Retry" or "Enter new password"

Selecting the new password resulted yesterday in a new box opening with this address ..https://account.live.com/App/Confirm?mkt=EN-US&uiflavor=host&id=292841&client_id=0000000040C8F39E&ru=https://login.live.com/oauth20_authoriz.

When I entered this in my browser yesterday I received a Microsoft message saying that the site was temporarily unavailable due to maintenance. Today at this juncture the box with this heading only appears momentarily but it is blank . I don't have time to copy the address. The connection fails again

Also yesterday access to my Outlook account was blocked because Microsoft thought the activity was suspicious. No doubt the sending of probably a hundred test messages over the last 2 weeks is the suspicious activity. Certain specific ISP addresses were blocked and I had to ask Microsoft to unblock them. Which they did. I hoped this might solve the problem but it didn't.

On my laptop I have newly installed Windows 10 and Thunderbird with just the outlook account. Nothing else other than Edge.

On my Windows 11 desktop I have an existing thunderbird app with yahoo and gmail accounts which use oauth2 with no problem. I have uninstalled thunderbird many times and also created a new profile to clear out any old rubbish etc. No matter what I do I cannot send an outlook message via thunderbird on either computer
Hornblower409 12,060 Reputation points

2026-07-19T14:31:00.1233333+00:00

@philip lightfoot said

No matter what I do I cannot send an outlook message via thunderbird on either computer

Sorry, I'm stumped. I can't reproduce so I can't debug.

yesterday access to my Outlook account was blocked because Microsoft thought the activity was suspicious. No doubt the sending of probably a hundred test messages over the last 2 weeks is the suspicious activity.

A few hundred messages a week is not usually enough to get you blocked. Any chance that someone else is using your outlook.com SMTP account for nefarious purposes.

I assume you can logon and use your outlook.com account in Outlook Web ( https://outlook.cloud.microsoft/ ) with no problems?

Just as a cross check, you might want to try testing with another email client. e.g. Free em Client for Windows That might tell us if the problem is your account or your client.
Lucus-V 10,425 Reputation points Microsoft External Staff Moderator

2026-07-19T15:24:32.16+00:00

Hi philip lightfoot,

Please note that our Microsoft Q&A forum is a public platform, and we will modify your response/ question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Please try connecting through your smartphone's mobile hotspot and see if the issue persists.

Additionally, as suggested by Hornblower409, you may want to try using a different email client to determine whether the issue is specific to your current one.
philip lightfoot 0 Reputation points

2026-07-19T20:21:32.7533333+00:00

Thank you for your suggestion both of you. I have tried using Mailbird. I got the same error on sending a message from Outlook in Malibird.

It was last Saturday and I spent all day on the problem on my desktop computer using the AI on Mozilla Firefox. I was led into all sorts of things like Config Editor in Thunderbird and making changes via the Registry. Changing things from False to True and then changing them back, checking values. etc. Eventually all avenues were covered. AI appearing very human concluded from all the checks that the problem was with Microsoft. I was recommended to add Owl for Exchange. It was now very late at night and I persevered with Owl for Exchange on the Sunday but I didn't get it to work. I can't remember what the actual problem was. I was pretty fed up by this time and just decided I would write outgoing messages using the web version but every time I deal with my mail I can't resist just trying an outgoing message in case something has changed and off I go again.

What frustrates me is, when testing the connection in the account settings.,outgoing server area, I get the message .. "Successfully established a secure connection to smtp-mail.outlook.com:587. " and I can view the test certificate. Microsoft has messaged me to say thunderbird has accessed my outlook account also - yet I still can't send messages.

The outlook account is only a few weeks old so I don't think anyone else could be using it.

Some people on Google recommend using the Classic Outlook.

I don't know if it is possible to download the classic version and how this will fit in in with the existing. I will look into this when I have more time.

I have moved to Outlook because my broadband provider is ending its mailbox service.
philip lightfoot 0 Reputation points

2026-07-19T20:32:58.55+00:00

I had just completed a lengthy reply saying I had tried Mailbird with the same result and also used Mozilla Firefox AI during a long session which lasted some 10 hours last Saturday. I said that AI had come to a conclusion and they advised me to add Owl for Exchange.

My reply has been deleted by an automated system.

Thank you both for your help. I will not pursue this further but just hope that sometime in the future the problem corrects itself. As I said in the reply I will use the web version for outgoing messages.

I hope this is not auto deleted.
philip lightfoot 0 Reputation points

2026-07-19T20:35:21.2233333+00:00

Well! what i said was inocuous.
philip lightfoot 0 Reputation points

2026-07-19T20:36:52.78+00:00

Thank you both. I will not pursue this further in light of being auto deleted twice
philip lightfoot 0 Reputation points

2026-07-19T20:40:25.3733333+00:00

I have tried an alternative client. I wont mention the name in case that deserves auto deletion. I had made a full reply which was time consuming.
Caozhi Li 7,350 Reputation points Volunteer Moderator

2026-07-19T21:14:50.93+00:00

sorry, false positive - restored :)
Hornblower409 12,060 Reputation points

2026-07-19T21:31:14.4233333+00:00

@philip lightfoot said

Some people on Google recommend using the Classic Outlook.

Classic Outlook is a paid product. Either MS 365 Subscription or Standalone. Please advise if you want more info.

The free alternative is New Outlook. Multi-platform.

Windows: https://apps.microsoft.com/detail/9nrx63209r7b
Android: https://play.google.com/store/apps/details?id=com.microsoft.office.outlook&hl=en
iOS: https://apps.apple.com/us/app/microsoft-outlook/id951937596
Mac: https://apps.apple.com/us/app/microsoft-outlook/id985367838

New Outlook for Windows is an easy install/setup and it's known to work almost flawlessly with an outlook.com email account. If New Outlook fails to send using your outlook.com account, Microsoft Support should be able to help.