Thunderbird Community Forum

I've successfully connected to a hosted Exchange server through EWS and NTLM authentication (kudos BTW). But there is a problem - often during operations against EWS I'm presented with "Login to account XXX failed" "Login to server YYY with account XXX failed". I can ignore it (cancel) and it will work for seconds or minutes but eventually reappear. Sometimes it's very frequent, sometimes is here and there. TL;DR; connection works, I can read directories and e-mails.

From looking at development tools I see these scenarios: 1. POST requests return 200 always (no messsage of course) 2. Eventually a POST would return 401. Then Thunderbird issues a GET, it returns 401 as well but response includes header WWW-Authenticate: NTLM XXXXXX. Then another GET is issued containing header "Authorization" with the value from previous response. This time it gets 200 and continues without POST requests without a dialog. 3. Sometimes there are more POST requests with 401 (I assume in parallel) before a GET is issued and then I see a dialog. Sometimes it recovers (regardless of whether I cancel or retry), sometimes gets stuck with 401 with dialog reappearing each time it tries something. This case it's similar in sense that thunderbird issues GET with 401 and WWW-Authenticate header, issues another GET with Authenticate header but still gets 401.

If I had to guess I'd say the problem happens when POST requests are issued in parallel, not sequentially. OTOH it might be a problem at the server, but it isn't very likely.

Hello, from time to time my Thunderbird on my desktop PC running windows 10 doesn't receive emails, while they arrived on my I Phone 8. Checked my Telstra web mail, all emails are there so what is stopping getting to my desktop PC? I thought the Thunderbird receives emails than synchronize with my I Phone? As you can see from my 2 images the Telstra is up to today as is my I phone But Thunderbird is 3 days beyond. Tomorrow it may back to normal or the next day? I am returning to this message the next day 16/06/2026 1 more message on my I Phone, still nothing on my Thunderbird.

An other problem I get with Thunderbird is that a message appears on the right bottom of my screen: "Mozilla Thunderbird Connection to server mail.bigpond.com timed out" and/or "failed to connect to mail server imap.telstra.com" If I try to send an email after the above notifications, I get the "Connection Refused". I know than to just walk away. I am using Starlink as Telstra here doesn't work as I am on the fringes of Melbourne in a BLACK HOLE. Any help will be gratefully received. Thank you for reading this. Regards Ilio Pieroni

Hi, Since approx. 1 month, I cannot receive nor send emails from my Windows 11 desktop computer. My ISP is Videotron and they tell me that from their end, everything is fine and the configuration is fine. If I use the Videotron Web Service, I can send and receive emails using the Videotron Web Services but these are not reflected on my Thunderbird email interface. If I try to send an email from Thinderbird, I get this message # # * * Sending of the message failed.

1. # * * An error occurred while sending mail: Outgoing server (SMTP) error. The server responded: smtp.videotron.ca Videotron ZGdcwFfPIz2we service temporarily unavailable AUP#EML-016.'

On my Android smartphone, Thunderbird is installed and it works perfectly...I can send and receive emails.

What can be done to make sure that I can send and receive emails from my computer, and to keep the smartphone and computer synchronized. Thank you

A category (Daily Brain something) of emails that are clearly spam (you even think they are spam) are landing in my Inbox every day. I have my email set to not allow emails from any addresses that aren't in my book. If I follow their 'unsubscribe' link, I just get more of them. This is the latest one: ar849137@ocotille.com with a Reply To address of: 3527_rep_Y2pnZGVzaWduc0BlYXJ0aGxpbmsubmV0@ocotille.com Every one is different. Why are these getting through? Thanks Cary

I've been using Thunderbird for years but suddenly as of yesterday it's stopped receiving messages. First it told me my password was incorrect. Ever since then when I try to click "Get Messages," it simply has no response at all. Nothing happens. I went into my Thunderbird password settings, and upon seeing that the incoming-message password had for some reason reverted to an old, obsolete password, I corrected it and saved the correct one. I've checked several times and the passwords are correctly saved now. But this did not fix the problem. When I click "Get Messages," nothing happens. My Thunderbird is connected to my Earthlink account, which is working fine. When I go into Earthlink, I am able to send and receive messages as normal. So the problem is not with Earthlink but with Thunderbird.

I just had a support session and the tech was unable to solve the problem. We tried installing a new version of Thunderbird and importing the messages over from the default install and it just freezes up. He tried replacing account settings with the account settings from a previous version and that didn't work either. He suggested contacting Mozilla to see if there was a way to import messages from the frozen default to my new profile.

When I add a calendar event, it defaults to Holidays in US. How do I change this to the calendar associated with my email address? I often forget to change the desired calendar. Also, How do I edit the Holidays calendar? Thanks BigSam

I am unable to send an email from Thunderbird to 2 hotmail accounts that I have been communicating with for several years. The issue has only recently started and I can send emails to them from another email account that I have on gmail and any other emails than these are fine from Thuderbird Below is the return message that I receive - can you help

   ""  This is an automatically generated Delivery Status Notification.      

Delivery to the following recipients failed permanently:

  * andyfmorris@hotmail.com

Reason: A message that you sent to the following recipient could not be delivered due to a permanent error. ** The remote server ?? responded with: ** andyfmorris@hotmail.com ??:?? This message was created automatically by mail delivery software on the server .

Reporting-MTA: dns; avasout-peh-004 [212.159.14.20] Received-From-MTA: dns; [192.168.1.81] [51.7.113.34] Arrival-Date: Tue, 17 Feb 2026 11:05:53 +0000

Final-recipient: rfc822; andyfmorris@hotmail.com Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [212.159.14.20] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BCD72C9602F57A] [DU2PEPF00028D0F.eurprd03.prod.outlook.com 2026-02-17T11:05:53.185Z 08DE6B964EE3CE26]

Last-attempt-Date: Tue, 17 Feb 2026 11:05:53 +0000 ""

Hello,

I can't receive any of my e-mails. I can send e-mails out now. Plus I can put in my password to log into my e-mail.  This has been a headache for me, I have been with Thunder Bird for years.

I also get a boxes that says : Unable to write the email to the mailbox. It says to make sure the file system allows me to write privileges, and I have enough disk space to copy the mailbox. I have enough space on my computer system and all. Another box that says my e-mail is being processed. Please wait until processing is complete to get messages. I did e-mail you yesterday on these issues. As I said I can e-mail messages out now also log into my e-mail with my password. Thanks, Chris

Please ask Thunderbird to stop making a tab on my taskbar every time I open an email. I have to close each one individually, and I never asked for these to be shown, and I don't need them shown. This is a tedious extra chore. I already have access to emails that I receive in my in box. It shows the history. I don't need any other index to them. Do you know how to stop making any other such tab or index? If not, please pass this on, and please don't say that you can't pass on this request. Someone decided to make these tabs show up on my screen and task bar, and to require me to close them by clicking on each little red X mark. I should be able to make contact with whoever makes these decisions and writes these programs, and to provide feedback and suggestions to them.

Thunderbird is not connecting with Xfinity Comcast for sending or receiving emails at gpenkala@comcast.net . This combination was working fine for decades. Last Friday (Jun 12) was the last email I received in Thunderbird. I can view current emails on the Xfinity website, but these are not being transferred to my Thunderbird account anymore, These are the error messages:

"Sending of the message failed.

Unable to authenticate to Outgoing server (SMTP) smtp.comcast.net. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'." "Sending of the message failed. An error occurred while sending mail: Outgoing server (SMTP) error. The server responded: resomta-c2p-555483.sys.comcast.net resomta-c2p-555483.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available."

Can you tell me what configurations I should be using within Thunderbird for Incoming and Outgoing Servers?

[6/12/26, 10:49:22 PM GMT-4] Applied filter "Blocked Sender List" to message from The Home Depot® Consumer Credit Card <citi@info15.citi.com> - James, Don’t forget to use this special offer to get your Summer projects going! 🌼🌺 at 6/12/26, 10:02:27 PM GMT-4 deleted

[6/12/26, 10:49:22 PM GMT-4] Filter action failed: "Move failed" with error code=0x8000FFFF while attempting: Applied filter "Blocked Sender List" to message from The Home Depot® Consumer Credit Card <citi@info15.citi.com> - James, Don’t forget to use this special offer to get your Summer projects going! 🌼🌺 at 6/12/26, 10:02:27 PM GMT-4 deleted

The sent message is deleted but I get Filter action Failed.

I recently updated windows and since then I have not been able to login to my emails and or recover contacts or calendar on thunderbird. I am able to login to my primary email but I have no contacts and am not able to login to my other 2 email accounts.

Hi all! I'm having an issue with Thunderbird in conjunction with my Outlook account.

I used to be able to add my account just fine (using OAuth2). But for a few months now, I have been getting "Authentication failed" errors (see first picture).

It used to be that I could temporarily remedy this by signing out and back in. Today, however, I was unable to sign back in, using the stock settings for Outlook (see second - fourth picture). No authentication popup appeared.

I was sporadically able to add the account and get messages to start appearing by clicking on "Edit configuration" and removing and re-adding the hostname for the IMAP server, without an authentication popup appearing. I therefore suspected that there might be some half-stale credentials stuck in the cache, and there probably were, because after clearing my cache this method doesn't work anymore. I am still not getting any authentication popup though.

All the usual suspects I already tried: Thunderbird is up-to-date (151.0.1), my Outlook account definitely has IMAP and SMTP activated, and another mail account (gmail) works without a hitch on the same system.

I hope that someone can help me, as I'm at my wit's end. Thanks in advance!