Thunderbird says "login failed" when trying to send an email

Microsoft stinks. That's why I am trying so hard to get Thunderbird to work. When I reply to an email in an email chain that I was the last to reply to, it responds to me. I need to reply to all, the remove myself. Thunderbird corrrectly responds to last person other than me.

I was downloading Office 365 before so I could try "Old Outlook". As I said, that failed. It worked today. Yay! I switched to the old layout. It's read only without a subscription. I had Office 2013. I have the codes, but it won't let me download it.

I think I will have to try Geek Squad again. Everything I search says it should work, but I have no idea how to find the setting.

You have been absolutely amazing. I don't know if you are a Mozilla employee, or just a very nice person, but I cannot tell how much I appreciate your help (and you keep some amazing hours on this forum... :) ).

Thank you.

I went to Geek Squad today. He said all the settings are correct. He found something with other people having the same issue. They said MS said they won't let it in immediately, but it should work in a week or two. I guess I'll find out.

That sounds very odd. The info below was sources from Mozilla blogs on this issue. Don't believe the word of a support rep over the phone as they are not engineering this protocol. Merely clearing the call que.

EWS (Exchange Web Services) email support has been available since Thunderbird 145, but Microsoft will shut down EWS for Microsoft 365/Exchange Online by Oct 2026 and will require switching to Microsoft Graph API

If you are connected via EWS to Microsoft 365, you will need to set up a new Microsoft Graph account before the shutdown.

Use the Correct Account Type

When adding your account:

   In Thunderbird, go to Menu ☰ → New Account → Email.

   Enter your Microsoft 365/Exchange email address and click Continue.

   Sign in via the Microsoft OAuth panel (do not type your password in Thunderbird).

   When prompted, choose Exchange or Microsoft Graph API (Graph is required for Microsoft 365 after 2026) 

   In short: For Microsoft 365/Exchange Online, Thunderbird now prefers the Microsoft Graph API over EWS. If you are blocked from Graph or your org still uses EWS, ensure you have Thunderbird 157+, update your account type, and use the official Microsoft OAuth sign‑in. For on‑premises Exchange, EWS will remain supported until 2027 Mozilla 

I hope this helps. You need to create a new password Somewhere.

We deleted the account and entered it again. At a point when sending an email it asks me to enter a password. When I click the button, Chrome opens and flashes, but stays on the webpage it was on. The first agent I spoke with a few days ago went somewhere and hit reset, and it then opened a page for me. No one since that person has been able to find that page.

I just changed my default browser to Edge and it does the same thing.

Thunderbird fills everything in for me. Where can I change it? Is it on that page I can't see?

Yeah I'd have to remote you at this point lol Good morning look in your browser settings on the spoked wheel page settings. Scroll to content settings and manage. Make sure you're allowing everything. I don't know if you have a third party pop-up blocker running in the system tray as an add-on in your browsers etc but yeah you're blocking it on your end.

But you're on the track that is what you need to do to get your emails to work you need to create a new profile and password. As far as your system is concerned with ad blockers whatnot that's something you will have to configure I don't even see a screenshot of your desktop at this point it is kind of difficult for me to guess

I steered you in the wrong direction on your settings by the way you want to click on the three dots at the top of the edge browser look into settings and then over to cookies and site permissions manage your extensions as well you may be blocking site redirects and that's why the page isn't displaying properly.

I'm sorry. I don't follow that at all. I see cookies, but no site permissions. There is a rocker to block third party cookies, but it's off.

I switched to Firefox, it let me get to the login page. I logged in, it said I was logged in, but Thunderbird still fails.

Unless you have a way of working with me that I can pay you for, I think I'm going to have to give up. As I've said before, you have been amazing and I am very grateful, but I don't see a way forward without a one-on-one.

Hi I hope you are doing well don't give up hope you will eventually solve your issue. Here through the Mozilla portal I would not use it as a source to draw customers this is a free help totally volunteer. I am curious as to what the error message reads on Thunderbird.

I get the first one when it fails. The second when I click cancel.

I changed my default browser back to Chrome, so I'm just getting the browswer flash when I click "Enter New Password".

When I switched to Firefox, I got a login page and used my PIN to log in. It said that worked.

In your Thunderbird account settings area at the bottom is the SMTP section you must update your password that you recently recreated on the MS Office 365 side. As far as your browsers you definitely must familiarize yourself with chrome to solve your issues I don't use Chrome.

Also be advised Thunderbird lacks native MAPI integration with Microsoft Word, and Microsoft 365 requires OAuth 2.0 authentication, which can block third-party add-ons from directly releasing queued mail. Ultimately ensure Thunderbird is set up using OAuth 2.0 for both IMAP and SMTP settings rather than basic authentication.

You may just have to use natively the Microsoft Office 365 interface if you can't get past the authentication glitches.

Also make sure you are not encrypting your password in thunderbird.

All you are mentioningare things that Geek Squad did. If I can't find someone who can screenshare and is infinitiely familiar with Thunderbird, I have to be done.

I fully trust the first person I worked with. He was able to clear whatever stops me from entering my password in Chrome and nothing he did changed anything. He was SO frustrated I had to leave.

I don't believe the person I need exists, so I have be done. I hate Outlook, but it seems to be my only option short of getting a email address from a different domain.

I will for the last time say how appreciative I am with your continued and quick attempts to help me. Google needs you.

Thank you so much...

You're welcome may I simply say it was a pleasure working with you I'm not sure if we're missing the mark through some small technical settings, but if I had an ISP that didn't offer email I would look elsewhere. Comcast is a big name maybe it's available in your area. However that's what I'm used to when I sign up for internet service and or television phone bundles the isp normally provides an email domain of some sort. So normally you would just populate your isp's POP3 and SMTP server addresses your account username and password and be done with it. Seems like your eyes pee is making you jump through loops for mail. You can use protonmail as an example rather than the 365 or gmail but in my experience if an internet service provider doesn't have an email server set up for its customers it is a clear sign to stay clear of that provider.