Thunderbird Community Forum

I am using Thunderbird Meadow.

Is it possible to send emails without a subject, other than getting the warning dialogue box.

It would be very useful.

Thank you

Bug report 15 Aug. 2026

The disappearing emails.

It took me a while to find out what was going on. My friend said some of his Sent mail was nowhere to be found. After searching for it in a 'wrong' place it does not exist. Sending to the same recipient and again it just disappears. Simplifying the mail down to just address and the word "test", it still disappears. No combination of a Thunderbird search nor an Everything search finds anything. No return error message from this provider nor the recipients.

This address is for the local electricity board, other mails to other departments

go through correctly and are found in the Sent email directory.

A careful inspection of the contact information shows this is the only department

without a "Shown Name" it only has an email address filled in.

Entering a Name for this contact solves the problem, it now shows up in the Sent

folder and is easily searchable.

I hope this explanation helps some one else with a 'Houdini' email.

My e-mail stopped downloading. It was working fine, I changed nothing, no error message. It accepts my password, cycles through it's process, then quits without downloading anything. Sending still seems to work.

We did relocate from home to my folks' in-between, but I've never had issues at their place before, and otherwise my connection to their wireless works fine.

I'm on TBird 153.0.2esr after a recent update. On previous versions the "Get Messages" button in the top left side of the menu's was working fine. When the button was selected, an update was displayed in the bottom left frame of the window. The update would say something like "Connecting to ..." and the message would be downloaded from the server. Great...

If there were no messages on the server, the update would display "There are no messages on the server". With this current version, I don't see any messages in the lower left frame of the window.

This is a convenient feature of the app, as I like to check the server for messages prior to shutting down. It's also convenient for getting messages with a security code without having to wait for the next scheduled message download. Now I can only assume there are no incoming messages when I push the button and don't see anything in my Inbox.

Dear Mozilla Development Team, Please reinstate this feature for upcoming versions of Thunderbird. Oh, BTW, this is a great app that I use daily for email. I use the calendar as a log book for my daily activities as well as an appointment scheduler. Thanks for your attention.

P.S. I see a new version is available (153.0.3esr) today (8/14/26), so I'll update and see if the same issue occurs.

Orange obliged me to have a new password to have an access to my mails , sending and receiving . But it does not work , and now I can only use Orange .What can I do ?

Coming from https://support.mozilla.org/en-US/kb/cannot-send-messages, and https://support.mozilla.org/en-US/questions/1596545#answer-1837376 (thank you christ1)

Account settings attached. I don't have an active firewall. My email provider is microsoft (outlook) No antivirus installed Linux Mint 22.3 x86_64 Thunderbird 153.0esr

I have confirmed with microsoft support that the ports and such are correct, they claim thunderbird is the problem.

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.

Im looking for help to set up my Hotmail account. I have 4 emails. They all worked perfectly for a long time. All of a sudden, everything just stopped. I have tried everything and the configuration seems to be correct. Ive tried every fix i could find. It just no longer makes sense to me. Does it just not work with Thunderbird? The specific message is "User is authenticated but not connected". Also when i tried to send an email, i get "Login to server smtp-mail.outlook.com with username **********@hotmail.com failed."

My email account [redacted from public] @live.co.uk was receiving mail until 6th August and then nothing. I'm getting a notification to say authentication failed and when I tap it the screen says "checking incoming server settings" and doesn't complete. I'm in the process of changing Web account logins from a talktalk account to the live account as the TT account is attracting spam. Could this have influenced the server settings?

Richard

Hello, I use Thunderbird to retrieve my AOL mail. Starting today, when I start Thunderbird it retrieves the AOL mail and then after a couple minutes I get the attached popup. I am not trying to connect Thunderbird to any Google account and I don't understand why I would get a message saying to use Google to sing in to Thunderbird. Once this popup occurs Thunderbird will not connect to AOL until I close it and restart it. I do have GMail set to forward messages my AOL address but this screen has not come up before

Any thoughts?

Thanks, John

It seems it is because BUGZILLA uses the AMAZON'S service, but there is now a RANGE of IP addresses that have been blocked, and BUGZILLA have been caught up in this mess. Please let me know which board I can use to report/ask about this issue, if it is no on here..

Here is the issue research (NOTE: I have emailed the BMO_MODS email several times, but had NO RESPONSE, so want to check if others have this issue):

Based on the error message you're receiving, Microsoft is blocking emails from your IP address because it appears on their block list. This is a Microsoft-specific issue rather than an AWS problem. When you receive a 550 5.7.1 error with the S3150 code from Microsoft domains (Hotmail, Outlook), it means Microsoft's filtering systems have identified your IP address as a source of problematic traffic. Even though you're using a managed dedicated IP and haven't intentionally violated any policies, there are several reasons this could occur: The IP address may have a poor reputation due to previous usage by another customer, spam complaints from recipients, high bounce rates, or sending patterns that Microsoft's algorithms flag as suspicious. Sometimes legitimate senders get caught in these filters. To resolve this issue, you should:

• Contact Microsoft directly using the troubleshooting link provided in the error message (mail.live.com/mail/troubleshooting.aspx) to request delisting
• Review your email sending practices to ensure you're following best practices (proper authentication, low complaint rates, engaged recipient lists)
• Consider contacting AWS Support to discuss your dedicated IP's reputation and whether a new IP might be warranted
• Ensure your SPF, DKIM, and DMARC records are properly configured Microsoft maintains their own independent block lists and reputation systems, so even with AWS's managed infrastructure, you may need to work directly with Microsoft to resolve deliverability issues to their domains.

I have thunderbird installed on my PC, and my main email account is a gmail account. I download from gmail using POP protocol (SSL/TLS connection security, OAuth2 authentication). I have been using these settings for a long time (15 years?).

This afternoon, thunderbird stopped downloading my messages. No error messages : just "no new messages to download".

I can see (by logging directly into my gmail account using my browser) that there are new messages on the server. They're not spam or junk, and they're not getting downloaded into my (local) spam folder. They're not getting downloaded at all.

I still have room on the google server (it's about 87% full), and room on the hard drive on my computer (about 3 GB).

Seems like soon as a batch of emails download they all open up immediately or at least as soon as I open or delete one they all open. Never had this happening until just late this week.

Incoming mail on my windows 11 computer has begun appearing in the Sent folder instead of the Inbox. It appears to have started 7/26/26. When I right click on the message I see an option to "move to inbox again".

  This does not happen on my Macbook.