See other threads. No solution so far. Probably an update bug.

pop account? who is your mail provider?

Also, (john only)

You've had version 141.0 for many days, and problem only just started? What AV software and extensions are used?

Wayne

I received notification of your response OK via Thunderbird. But problem continues as detailed below.

I use POP email in Thunderbird since 2005. Bitdefender AV. Thunderbird allows virus scan. No virus found.

Extensions

   AttachmentExtractor (disabled)
   ImportExportTools (disabled)

I updated to Thunderbird 141.0 after the problem started, thinking that might solve it. It did not. So the problem occurs on 2 versions.

I recently cleaned my inbox and my sent box of unimportant emails, then compressed and ran file repair on them. The problem occurred after that.

- All received emails are good in AOL webmail including ones I sent from Thunderbird. - Emails sent to myself from my AOL address via Thunderbird are bad received in Thunderbird - Emails sent to myself from my business addr via Thunderbird are good received in Thunderbird - Emails sent from AOL webmail to myself are bad as received in Thunderbird - The sign-on auth email from AOL is bad as received in Thunderbird.

- I did an HP UEFI full sys diagnostics. All passed. - I did a Bitdefender full sys scan. No issues.

I can send example emails showing eml and source HTML, but I would need to convert them to jpg images for upload here. Let me know if this would help

John

> I updated to Thunderbird 141.0 after the problem started, thinking that might solve it. It did not. So the problem occurs on 2 versions.

So also version 139 and 140? In other words approximately two months?

Does problem change if you do Help > Troubleshoot mode?

Wayne

The problem started Monday 8/11/25. I think I was on version 138, so I updated to 141. No improvement.

Per your suggestion above, I tried Troubleshoot mode. No improvement.

I also just now tried formatting a test email in plain text only. It still fails. With or without HTML the received email has blank subject and from fields. When opened, it starts with a long DKIM signature (X-SONIC-DKIM-SIGN), then HTML. In my plain text test email, it starts with a long DKIM signature then plain text.

I just noticed that the good emails have a much shorter DKIM signature than the bad ones. I don't know if this is relevant.

John

So I created a new profile from scratch in a new Thunderbird folder after renaming the old one. I didn't import anything. At first, it looked good. Emails previously received bad were now repopulated good in the inbox from the AOL server. But when I sent an email to myself from my AOL account in Thunderbird, the same problem appeared.

I don't know what else to do.

I did a complete HP laptop system diagnosis, complete system virus scan, uninstalled and reinstalled Thunderbird, created a new profile from scratch. I don't see anything else I can do. Maybe go back to an earlier version of Thunderbird? Go back to a previous Windows 11 system backup? Buy a new computer and switch email clients and switch to gmail?

I can't spend full time on this much longer. I have other problems to solve in my life.

I started experiencing this exact problem at the same time, on 8/11.

I have been using the same setup for YEARS with no problems. Running Thunderbird on Windows 10, accessing an email account at Earthlink using POP3.

On 8/11, suddenly most (but not all) downloaded emails appeared with blank lines in the Inbox list (i.e. no sender, subject line, etc), and the message body consisting of the HTML source code of the message. There does not seem to be any definite consistency as to which emails are downloaded normally and which are downloaded as source code.

Immediately prior to the appearance of this problem I had not installed any recent updates to Thunderbird or Windows. Since it began I have updated Thunderbird to 140.1.1esr (32-bit) and installed the latest Windows 10 update, which had no effect.

When I access the Earthlink mailbox directly using Earthlink's webmail, all the messages appear normally. And when I access the mailbox using IMAP from an Android phone, all the messages appear normally. As far as I can tell, the problem only occurs when downloading emails via POP3. I have not tried using another POP3 client yet to see whether the problem occurs only with Thunderbird.

It is not 100 percent clear to me from your posts where your mailbox is located, but if your email provider is someone other than Earthlink, that would tend to rule out Earthlink's POP3 service as the cause of the problem. I also appreciate the info you have provided on attempted fixes that did NOT work -- as it spares me from trying those things!

Staying tuned to this thread ...

You use bitdefender?

Please read wsmwk post and possible workaround at https://www.reddit.com/r/Thunderbird/comments/1mo693n/comment/n8ammvq/

Please post your results - does the workaround work for you?

My emails work now! No change needed to Bitdefender. I changed my SMTP server from my business email server (which worked for years) to smtp.aol.com. I found online that AOL now requires OAuth2 authentication method. I tried setting that in Thunderbird (POP3, connection security SSL/TLS, Authentication method OAuth2) in both the Server Settings and Outgoing Server. When I tried to send an email, it opened my browser with a request for a password. It complained that the browser does not allow third party cookies. I tried a couple of times with my two passwords for AOL (one for webmail and one for POP and SMTP in Thunderbird). Then I realized it was asking for my laptop device startup password, which worked. I didn't think I succeeded in implementing security for OAuth2, so I changed my Thunderbird settings back to SSL/TLS Normal password while staying with smtp.aol.com. Now my test emails work from AOL in Thunderbird to both my AOL and my business accounts in Thunderbird. Test emails also work from my business account in Thunderbird. So the problem for me may have been the AOL configuration. I am not sure what solved it, but my attempt at OAuth2 and/or my change to smtp.aol.com seems to have worked, even though I am back to SSL/TLS Normal password.

Wayne: Thanks. I looked at your link re bitdefender. I do have Encrypted web scan enabled. It has always worked, and now works after the above efforts. The originator of that Reddit thread (LCARSgfx) had the exact same problem as myself and dpercival the next day after ours. The three of us use different email providers. So I don't know if it is an AOL problem or a Thunderbird problem. Maybe all email providers switched to OAuth2 at the same time and you just have to set OAuth2 and enter a browser-prompted password once.

dpercival: Please pose a follow-up if you try OAuth2 authentication.

Looks like the Bitdefender issue has been addressed now. I switched back to former Bitdefender settings (see workaround) today and so far all is OK.

My emails work now! No change needed to Bitdefender. I changed my SMTP server from my business email server (which worked for years) to smtp.aol.com. I found online that AOL now requires OAuth2 authentication method. I tried setting that in Thunderbird (POP3, connection security SSL/TLS, Authentication method OAuth2) in both the Server Settings and Outgoing Server. When I tried to send an email, it opened my browser with a request for a password. It complained that the browser does not allow third party cookies. ... Wayne: Thanks. I looked at your link re bitdefender. I do have Encrypted web scan enabled. It has always worked, and now works after the above efforts. The originator of that Reddit thread (LCARSgfx) had the exact same problem as myself and dpercival the next day after ours. The three of us use different email providers. So I don't know if it is an AOL problem or a Thunderbird problem. Maybe all email providers switched to OAuth2 at the same time and you just have to set OAuth2 and enter a browser-prompted password once. ...

Hard to say at this point because bitdefender may have already updated on your machine. That said, because your problem started on 8/11 I have little doubt that bitdefender was involved.

The following is what I have posted today in other user questions ... Solution update posted at 8:48 Eastern time (12:48 UTC) Thursday by Alexlandru_BD, an admin at bitdefender, "The developers reverted the changes made in the last signature update and this should do the trick until a permanent fix is deployed. Just click on update in systray and reboot once completed. But keep in mind this change is being rolled out gradually, so it may not reach everyone at the same time.." More details at https://www.reddit.com/r/Thunderbird/comments/1mo693n/comment/n8ammvq/

I've had the same problem since 8/11/2025, and I also use Bitdefender. Based on posts on here I tried saving the message to my Windows 11 machine, then edited it to remove the blank lines. I then opened the message using Thunderbird and it opened perfectly, including headers. I also opened the "unrepaired" file, and that opened as text. I then did the same with an earlier message from the same sender which I had no problem opening, and compared the text of both messages. The original files of both of them had the same blank lines, the only difference was that they were added to my messages by different versions of Thunderbird. I'm not seeing where you give me the capability to edit the file once it has been downloaded, so I don't know if removing the blank lines in the message file will fix the problem in version 141.

For right now, I've uninstalled Thunderbird, then installed version 137.02 and turned off automatic updating. I haven't had a problem since, but I would like to update to the current version once this issue is fixed. I don't see where Bitdefender would be the problem, since the files looked identical on the earlier version but opened perfectly.

Please let me know when this is resolved. I've also opened a support ticket on Bitdefender for the same issue and will let you know if they find anything.

Steven

Steven, bitdefender pushed out a fix, so you shouldn't see the problem on any versoin of Thunderbird.

And unless new information comes to light, we do not have a flaw in Thunderbird, so I do not expect any fixes via Thunderbird updates.

If you learn more about your situation, pleaes create a new questions https://support.mozilla.org/en-US/questions/new/thunderbird