All Products Community Forum

bob.fannon

Feb 14, 2026, 13:01 CST

I have used Thunderbird for a number of years with Plusnet (using POP settings) in the UK. However, Plusnet has transferred their support to a company called Greenby who have made a hash of it and offer very poor support. So, I want to use Outlook as the mail server but I am unable to send any messages via Thunderbird to the Outlook server. I can however download messages with no problems. The error message I get is :- Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.office365.com. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'

My default Outgoing Sever settings are :- Server Name : smtp.office365.com Port: 587 User Name: bob.fannon@outlook.com Authentication method: OAuth2 Connection Security: STARTTLS

I have tried deleting the Thunderbird account and re-creating it but still got the same result. I also tried to use my old Icloud account ( having first setup my App Specific password) but got the same result.

Windows 11 been working ok for years........incoming emails ok. Now emails outgoing.. not working since last update. Can Type a message and hit Send.........but its not received or opened at the other end. Is there a configuration or filter problem cutting in ??( keep it simple..old guy 80 yrs .).barry

Dear Support Team,

I am experiencing problems logging in to my Onet email account. The issue occurs when I try to access my mailbox, particularly through Mozilla Thunderbird.

Could you please let me know what might be causing this issue? Is there any specific configuration required in my Onet account settings before logging in?

Additionally, do I need to reconfigure any settings in Thunderbird (such as incoming/outgoing server settings, ports, SSL/TLS, or authentication method) to ensure successful login?

I would also like to mention that I do not experience any login issues when using email accounts from Wirtualna Polska (WP/O2) or Gmail in Thunderbird. The problem seems to occur only with my Onet account.

Please let me know if you need any additional details from my side. I would appreciate your guidance on how to resolve this issue as soon as possible.

Kind regards, Konrad

I recently lost incoming emails to my inbox. I am in the process of setting up a website and had to change the DNS settings to proceed with the website. Since then I have lost incoming emails to my Firefox email. Which also references the domain name. I'm not technical at all so I'm wondering what I need to try to get back to access. I'm wondering if it's something to do with the outgoing server settings ? Any help much appreciated, thanks.

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, can someone please fix this e-mail address please & thank you.

Following the instructions provided at this web page: https://developer.mozilla.org/en-US/docs/MDN/Community/Community_Participation_Guidelines I e-mailed a code of conduct violation report to the provided email address, mdn-cpg-report@mozilla.com

Actual results:

I immediately received the following e-mail reply, telling me in effect that my e-mail could not be delivered:

Subject: Delivery Status Notification (Failure) Date: Sun, 15 Feb 2026 21:34:30 -0800 (PST) From: Mail Delivery Subsystem <mailer-daemon@googlemail.com> To: [redacted]

Hello [redacted],

We're writing to let you know that the group you tried to contact (mdn-cpg-report) may not exist, or you may not have permission to post messages to the group. A few more details on why you weren't able to post:

You might have spelled or formatted the group name incorrectly. The owner of the group may have removed this group. You may need to join the group before receiving permission to post. This group may not be open to posting. If you have questions related to this or any other Google Group, visit the Help Center at https://support.google.com/a/mozilla.com/bin/topic.py?topic=25838.

Thanks,

mozilla.com admins

[headers, etc redacted]

Expected results:

I expected instead to receive a reply telling me that my e-mail had been successfully received.

I have been using Mozilla Thunderbird for decades and they have even contributed a small amount of money to Thunderbird periodically. Just within the last two or three days all of a sudden I have been unable to send emails with my phone. I receive emails, but I do not send them. So I opened up a laptop where I did not have Thunderbird and set it up properly through Spectrum using the incoming and outgoing servers as mail.twc.com. and yes, just like on my phone. I continue to receive new emails, but even with the laptop I was unable to send an email. I received the message"send message error sending a message failed. The message could not be sent because the connection to outgoing server smtp mail.twc.com was lost in the middle of the transaction. Try again."I contacted Spectrum twice and both times they had me try to send a message through their Web server spectrum.net and that message did go through. Of course then their response is that this has to be a problem with the third-party app meaning Mozilla Thunderbird, and they can’t help with that at all. I sure would appreciate some help because I hate to walk away from Thunderbird as well as change my email address after all of these decades.

Trying to send mailmerge. Thunderbird version 147.0.2 (64-bit) I have sent a mailmerge from thunderbird before, so it should work. I have my CSV ready, and I type the email draft. I click the mailmerge icon, and fill out the mail merge dialogue box. After I fill out Mail Merge dialog box and click send, a blank dialog box opens, then I can't do anything (my email draft is frozen)tried sending, and saving, or pressing load (all options highlighted in screenshot). See also screenshot of blank dialogue box and frozen message. I tried closing the blank dialogue box, but the mailmerge is not sent, and after that, I can create a new message, but the mail merge option is greyed out, so I cannot select it. So I shut down Thunderbird and restart, then I can click the mail mergeicon,but same problem,I only get as far as the blank dialogue box. Thank you so much for your help

Hello, I only use Thunderbird on my PC with IMAP. For the past three days, while I receive my emails just fine, I can no longer send them. They bounce back with the following error message:

The only thing I've done is also install Thunderbird on my mobile phone. It asked me for a password that I don't know and don't think I've ever had one for Thunderbird.

However, when I go directly to the Free Zimbra website associated with my email, it works and I can send my emails. Thank you for your help.

Christian - Error message attached.

My Thunderbird email account no longer lets me send out messages. I get a message error

  QUOTE____

Sending of message failed. An error occurred while sending mail. The mail server has responded. Message contains bare CR and is violating 822.bis section 2.3. Please check the message and try again.

But I am able to receive messages.

Can anyone help. Thanks in advance!!

My Thunderbird hasn't downloaded emails to my main/default address since mid January. The other two addresses, with all the same settings, and with the same provider, work. Emails are goint to my web mail. I've spent hours on support and on remote control with my provider, and they finally said maybe it's a thunderbird problem. I deleted the programme and reinstalled it, still won't download and all the emails are still missing from my inbox. The emails went missing when I attempted to repair the folders earlier in the saga.. All my local folders are there. I may have to start all over again from a new programme. Thank goodness I can access all emails from my provider's web portal. Aussiebroadband.

Hello,

I'm trying to setup a new GMX email address in Thunderbird. I can receive messages, but when I try sending an email, I get stuck on the loading bar "sending message". I receive no error message.

I have multiple GMX addresses in Thunderbird already, all work well for receiving and sending emails. I tried writing to email addresses with different providers, the result is always the same.

I tried adding the IMAP info manually and automatically in Thunderbird, nothing changes. Here is my current SMTP server :

mail.gmx.com Port 465 SSL/TLS Normal password

Can someone please help me figure out this SMTP setup ?

Thanks ! Alix

I have a wordpress website and from time to time the emails in my TB 'inbox' will disappear and appear in my website as posts. My wordpress email used to be the same email but I have changed it and the problem still persists.

my server is charter.net never had a problem with thunderbird and then several months ago i stopped being able to reply to emails

Something horrible and time-consuming has changed within this past week to Thunderbird. My version is 140.7 1esr 64bit. Over the past 4 days or so, I've found I cannot scroll down and see the full emails--until I have to use this new pop-up system.

This is definitely not an improvement in my estimation. Is there any way to undo this?

I have been using Thunderbird for many years. I just got a new computer and installed Thunderbird onto it. I have several email accounts for personal, business and clubs so this makes it easy to keep track of. I have some gmail accounts and 3 different yahoo accounts. Now when I get an email to one yahoo account it prorogates to the other two. This never happened on the old computer do you have any idea how this happened, and more importantly, how do I stop it?

My address appears in From field when mail comes from someone else. Error message at the bottom says, "A unique identity matching the From Address was not found. The message will be sent using the current From field"

Re: Thunderbird

I have logged in on my mobile and a secondary laptop - however the folders on the primary device are not reflected; how can I get them to sync?

Thank you