Thunderbird Community Forum

Using Thunderbird 115.18.0esr Supernova 64-bit on Mac laptop OS 10.13.6. Worked fine for years, with ongoing Thunderbird updates, even though Mac OS is 32-bit. Suddenly, after 10/6/26 can't retrieve emails although I can see them on the ATT Yahoo server website. Can still send emails with Thunderbird. Inbound server settings are: POP server inbound.att.net, Port 995, SSL/TLS, Normal Password (I long ago created a Secure Mail Key, and even tried creating a new one). But inbound server name doesn't show in Saved Passwords (only outbound server with Secure Mail Key as password)? I have tried everything suggested, repaired my inbox folder, updated Thunderbird files, etc. in Profile as recommended. But still no prompt for password when attempting to get messages. Just shows "Done" at bottom left with no new messages received. But new messages are seen on server website. So it appears that Thunderbird isn't able to connect to the ATT Yahoo server to get emails. Why? And what else can I do? I love Thunderbird and want to continue using it.

ever since last update... can't send emails

Send Message Error Sending of the message failed. An error occurred while sending mail. The mail server responded: E5rTxqhwZYbiPE5rUxBTZm DMARC Policy Enforcement: https://postmaster.comcast.net/smtp-error-codes.php#ODM00001. Please check the message and try again.

Not sure what is going on but all of the sudden my inbound server is not allowing emails in. Outbound works. AT&T says its a Thunderbird issue. My computer guy cannot figure it out. Help. I can only receive email on AT&T

Connection error: Certificates. Works, doesn't work Thunderbird 157 intermittently fails to connect to imap.shaw.ca:993 with SEC_ERROR_UNKNOWN_ISSUER. It affects two separate Shaw email accounts, while Shaw Webmail continues to work normally.

Installed a week ago to replace MS365/ outlook Worked fine. But now it's acting up. Both my Shaw emails as well as my wife's email on her computer.

This does not happen with my domain emails.

My eMail has worked fine for many years - until this morning.

 When I first tried to "get messages", I got a response, "connection to inbound.att.net server reset".
 I restarted Thunderbird, and then the computer (Windows 11), and when I tried again, I got, ""inbound.att.net (POP) .. certificate revoked".
 I can login to my ATT webmail, but I can't download eMail to my computer via Thunderbird.

... In my attempt to upload this question, I looked for the TB Version, but it said to update Thunderbird. I did so, not it is back to telling me "connection...reset"

 Please help!

when trying to download email today, says certificate for inbound.att.net is not trusted. android email and browser email are OK.

when composing outbound email message ATTACH key is at top right hand corner of screen. If attachment is required and ATTCH key is clicked choice of File(s) or Webpage shows. If File(s) option is clicked Home -File Explorer comes up from which required file can be selected. This function has recently ceased to work. How can I reactivate the ATTACH function? Please assist, thank you, Chris

I have multiple email accounts on Thunderbird (on MX Linux)... att.net, gmail.com and aol.com

While traveling without my computer, i had to reset my aol password on my iphone.

Now that I'm back at my desk, and being unable to find how to change the aol password on Thunderbird, I deleted the AOL imap account and have tried much of today to add a new AOL account.

In the past, I could create an 'app password' within AOL (browser) and use that password in Thunderbird... but that is no longer working.

Any guidance/suggestions?

I am running the latest Thunderbird version 140.17.0esr (64-bit) available in my MX Linux.

I want to attach a file to an email. However, the ‘Attach’ button isn’t responding. The help button at the bottom of the page isn’t responding either. This hasn’t been a problem before.

Ich will an eine Email eine Datei anhängen. Der Button "Abhänge" reagiert aber nicht. Auch der Hinweisbutton an der Fußleitse reagiert nicht. Bisher war dies kein Problem

I'd like to resize an embedded image in an email. The bottom right handle is on the far right side. If I attempt to hover over the handle a scrollbar obscures the handle: it is not possible to grab it and resize the image.

How do I resize large images in Thunderbird emails?

Bonjour, Sitot la version 150.0.1 installée automatiquement, je ne peux plus ajouter de pièces jointes. Merci de debugger

Cordialement**

Brigitte Moulin

My inbox is not updating for my personal or work account. I recently reset the password for my company account and since then I have not received new emails on thunderbird.

I recently set up Thunderbird for Windows as a troubleshooting step for my Yahoo Mail account which has been generating an incessant number of authentication pop-ups in Microsoft Outlook (Classic) for Windows. I had been using New Outlook for many months before switching to Classic Outlook a couple of weeks ago. With New Outlook, there had been no authentication issues nor pop-ups appearing. I have been using the OAuth authentication, not app passwords, in all cases.

Setup within Thunderbird was relatively easy and the OAuth authentication went through without issues. The account has synchronized and seems to be continuing to do so as I read, delete, and send messages.

However, when I went in to the Activity Manager, I'm seeing a number of errors, appearing every 10-15 minutes or so. They read as follows:

• Alert from account xxx@yahoo.com: AUTHENTICATE Server error - Please try again later

• The current operation on 'Inbox' did not succeed. The mail server for account xxx@yahoo.com responded: UID FETCH completed.

• The current operation on 'Inbox' did not succeed. The mail server for account xxx@yahoo.com responded: p.

Can anyone help me understand what they mean? It would help me stabilize Thunderbird and might give some clues as to what is happening in Outlook Classic for me. It would seem some have authentication issues with Yahoo on different platforms while the service works perfectly fine for others. I would like to move away from Yahoo as I find it finicky with a number of its features, but I'm a long-term user (25+ years) and don't see that being a practical solution at the moment.

Thanks!

Yesterday, Oct 6, at 3:20 pm, tbird was unable to download messages from my att server. The error message is "The certificate for inbound.att.net does not come from a trusted source". Nothing that I know of has changed when I look at the account settings.

Do I need to contact Att/Yahoo? If so, how can I describe what to tell them, as I have no knowledge of certificates and how they work (or don't work).

I am assisting an elderly user with a personal @hotmail.com account that receives email successfully in Thunderbird but cannot send. I have confirmed they can send and receive emails from their online outlook.com portal. The user's computer setup is as follows:

• Windows 11 (with latest updates).
• Thunderbird 153.0.2 (64-bit).
• A personal @hotmail.com account with the following server configurations:

  -> Incoming IMAP: outlook.office365.com, port 993, SSL/TLS, OAuth2, and
  -> Outgoing SMTP: smtp-mail.outlook.com, port 587, STARTTLS, OAuth2.

Thunderbird successfully authenticates to Microsoft using OAuth2 for incoming email. However, when Thunderbird attempts outgoing email authentication, Microsoft's SMTP server rejects the authentication. The Error Console in Thunderbird records this message: "535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox."

-> Refer to attached image: "Thunderbird Error Console_20260811.jpg". -> I am able to provide a short screen recording demonstrating the failure if needed.

To try and resolve the above, I completed the following actions:

1. Confirmed Thunderbird is current (153.0.2).
2. Confirmed SMTP is configured for OAuth2 rather than Normal Password.
3. Confirmed port 587 and STARTTLS.
4. Re-authorised the Microsoft account/OAuth connection.
5. Confirmed IMAP OAuth2 works.
6. Confirmed Outlook.com webmail can send successfully.
7. Reviewed Mozilla's current “Microsoft OAuth Authentication and Thunderbird in 2026” guidance, including the section covering cases where IMAP/POP works but SMTP does not.
8. Captured the SMTP failure in Thunderbird's Error Console.

However nothing worked, so I raised the matter with Microsoft support and eventually had the matter referred to their Tier 2 team. The Microsoft case number is: 7107041963.

Microsoft Support confirmed that for a personal Outlook.com/Hotmail account there is no user-accessible mailbox-level SMTP AUTH setting, and advised that SMTP is enabled by default for supported clients. However, because sending from Outlook.com webmail works, Microsoft Tier 2 declined to investigate the SMTP server response further and directed me to Thunderbird support.

I am able to provide a copy of the chat transcript if needed.

In any event, the TLDR version IMAP works using OAuth2, but SMTP using OAuth2 fails because Microsoft's SMTP server reports SmtpClientAuthentication is disabled for the Mailbox. Microsoft Tier 2 has referred the issue to Thunderbird support.

Questions:

1. Is this a known current issue affecting personal Outlook.com/Hotmail accounts using Thunderbird?
2. Is 535 5.7.139 SmtpClientAuthentication is disabled for the Mailbox known to occur with Thunderbird OAuth2 even though IMAP OAuth2 succeeds?
3. Is there a current Thunderbird-side workaround or alternative SMTP server/configuration recommended for personal Hotmail accounts?
4. Would changing the SMTP server from smtp-mail.outlook.com to smtp.office365.com be appropriate for a personal Hotmail account in Thunderbird 153, or should the current Microsoft-documented server be retained?

-> I note there appears to be conflicting advice on this point in previous support threads.

1. Given that IMAP OAuth2 authentication succeeds for the same Microsoft account, does this indicate that Thunderbird's Microsoft OAuth authorisation itself is functioning correctly, or could SMTP require a separate permission/token that may be failing?
2. Are there any additional Thunderbird logs or diagnostics I can provide that would help resolve this matter?

Disclosure: I used ChatGPT to help organise my troubleshooting notes and technical details for this post. The troubleshooting, observations and diagnostic information described above are from my own work on the affected PC.