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My business has two domains. I can send email to a Gmail account holder using the primary domain with no issues. But amy emails from what I call the "secondary" domain below are treated as spam. This occurs with two different email addresses using the secondary domain.

Both domains are hosted with Bluehost. Exhaustive research has revealed the following:

• Settings in Thunderbird are exactly the same, e.g. ports, security, SSL/TLS, etc. for each domain.
• There is no subject line or content that could possibly be regarded as spam.
• MXToolbox indicates that the secondary domain is not on any blacklist.
• Extended support via Bluehost reveals that SPF, DKIM, and DMARC records are all correct.
• Email sent to a Gmail account using the CPanel (Roundcube) is not flagged as spam. Only emails sent via Thunderbird are flagged.
• Emails sent to a Gmail account from the secondary domain using my mobile phone, but still on the same network/IP address, are not flagged as spam.
• If I first send an email to one of the secondary domain emails FROM Gmail, then reply to it, the reply is not flagged as spam.

After many hours of head scratching (and later, head banging), I am pretty much at my wit's end with this problem. I'm an electronic engineer but this one is definitely out of my wheelhouse. Any help would most certainly be appreciated!

Thanks in advance, Don

Hi, I've been using Thunderbird latest version for a few days. Too much I have a problem that is bothering me. I have 20 accounts and if I choose Unified Folders, on the six of Tunderbird I see only a part of the Accounts and precisely 14. To solve my problem I also used the "Unified Folder Debugging" add-on but it didn't solve the problem. Why do I have this problem? I would like to use Unified Folders but I can't do it because I don't have any Accounts. Thanks for some info.

I have 4 email account. One account will not allow me to delete or send to junk box. When I press delete nothing happens. The emails (at least 30) that came in are marked junk too. The other 3 account work fine. I have had these 4 account for years and never had a problem. I have done a complete scan with Norton and nothing came up. Thank You in advance

I have 3 different hotmail accounts. And tried to set them up in a newly installed thunderbird app on windows (10,sorry not up to date). In the beginning I had 2 out of 3 working, but the last one is my business account and it didn't connect. I tried many different ways to get it working, and now only the 1st one is still connecting correctly. The second one also doesn't connect anymore and is giving me the: "The connection was refused when attempting to contact localhost." or Authentication error: Unable to log in at server. Probably wrong configuration, username or password.

I know for sure password and username are correct. I have added thunderbird to exceptions in firewall. I also tried turning the firewall off. no changes. I have no idea where it got so messy but can someone guide me in this? Most of it I do not understand so it is obvious I made mistakes.

After updating Thunderbird to version 150.0.2, I can no longer connect to my lolipop.jp mail servers.

Symptoms:

• Both IMAP and SMTP stopped working at the same time
• Webmail works normally
• Multiple mail accounts are affected
• Thunderbird times out when connecting to the servers
• The issue started immediately after updating to Thunderbird 150.0.2

Settings tested:

• IMAP: imap.lolipop.jp / Port 993 / SSL-TLS / Normal password
• SMTP: smtp.lolipop.jp / Port 465 SSL-TLS and Port 587 STARTTLS
• Tried Thunderbird Safe Mode
• Tried reinstalling Thunderbird
• Tried disabling Norton security/firewall temporarily
• Same issue persists

Could this be a known issue with Thunderbird 150.0.2? If so, is there any workaround or planned fix?

Thank you.

I just replaced my WiFi router and was able to get 5 messages after new network set up, but now it can't connect to outgoing or incoming mail server.. I double checked all my setting with Spectrum and all looks good, but won't connect.

I have filled in an un-correct password a number of times due to incorrect language setting of my keyboard. Then the popup window for this disappeared, and I cannot find a place to enter password. What can I do? It is the password for outgoing email.

I had TB on my desktop for years and finally got it also synced to my phone. Then with a failure with Windows 11 had to wipe clean the desktop and start over. Cannot reinstall TB. I obviously have the correct e-mail and password as I was able to log into Mozilla and submit this question. I believe it is a problem with my user name and what is on my phone setup does not work with my desktop reinstallation.

I have been trying to add my accounts to Thunderbird and had good success with gmail but wasn't able for Microsoft accounts. As I said in another thread (can't find the message anymore), I have 2 microsoft email account (one live.ca and one hotmail.com) and they both don't work. I was able to add them in Outlook desktop app and EM Client (a non open source software i'd rather not use) through IMAP with success. IMAP is activated in both accounts and as per Microsoft documentation the server is supposed to be outlook.office365.com on port 993. eM Client magically discover IMAP settings to imap-mail.outlook.com instead. Thunderbird opens an OAuth page and then it redirects from microsoftonline.com to localhost and fail with "Unable to connect".

2FA not activated in one account, if that matters. I have nothing running on port 80 if that matters.

I am running Windows 11 Pro 25H2. After updating Thunderbird recently to the latest version, it is crashing immediately upon starting Thunderbird, not even bringing up the initial screen.

The message is

"Thunderbird has stopped working. A problem caused the program to stop working correctly. Please close the program."

In addition, it brings up the Mozilla Crash Reporter, which states

"We are sorry

Thunderbird had a problem and crashed. We will try to restore your tabs and windows when it restarts."

I do not want to lose all my old POP3 messages, etc.

Please help, Nina

Hi - I can't seem to delete from my Yahoo Mail via Thunderbird.

With Yahoo's new mailbox limits I wanted to clean up my Yahoo mail box and Yahoo obviously does not provide any decent tools to support search and delete.

I downloaded Thunderbird and despite several deletion attempts my Yahoo mailbox still shows 160,000 emails whilst my Thunderbird client only 9,000 - so when I delete it is not syncing.

Most emails are deleted from Thunderbird however some are now reappearing (in Thunderbird). No deletions from Thunderbird are reachign my Yahoo mail inbox, however I can send emails from Thunderbird and see the sent and received email in Yahoo and I can add folders in Thunderbird and see those folders in Yahoo.

I tried several things

- immeadiate delete in Thunderbird - moving the emails to a folder in Thunderbird and then deleting from that and then deleting the the folder - I check this article https://support.mozilla.org/en-US/kb/thunderbird-and-yahoo and everything appears correct

I've had to pay for extra storage to get the code to make this post.

Mike

With 03.04.2026 they began to notice that the attached emails in eml format (the attached emails have attached documents, mostly pdf) sent from yandex mail stopped opening. Everything used to open well. Eml also does not save to disk. If you send the same files via Gmail, everything opens. Program version 150.0.1

OS: GNU/Linux Thunderbird Desktop

Is it possible to set up a TLS client certificate for authentication with SMTP, as it is with IMAP?

It works fine on the K-9 Android client for both IMAP and SMTP.

Is there a reason why this hasn't yet been added as an authentication method for SMTP?

Thank you!

Best Regards

I upgraded my Fedora nad I think that Thunderbird 149 came with that upgrade. I cannot send mails. Ctrl+enter has no reaction. Downgraded to 148 and everyhing is fine. |<