Thunderbird Community Forum

I'm getting a popup error message saying "Unable to write the email to the mailbox" on one of my gmail accounts. This has happened a few times before and I'm not sure how I managed to get it working again those times, seems hit-or-miss. I've compacted and run a repair on the inbox folder several times as suggested by others. I've updated and restarted Thunderbird and even updated windows and restarted more than once.

Windows 11 Pro Thunderbird 158.0 (64 bit)

I'm attaching a screenshot from the Error Console (Tools -> Developer Tools -> Error Console)

I've received the following message the last few days when I send an email with Thunderbird:

Your message was sent but a copy was not placed in your sent folder (Sent) due to network or file access errors. (I am sure neither of those errors apply.)

It then gave me the option to "save" (I didn't get the exact wording before I clicked on "save") and I don't see it anywhere. This was a very important email and I need to find it.

Hello, I recently converted a very large OLM (Legacy Outlook on Mac) to Thunderbird on my Macbook. I added an Office365 (work) Account to Thunderbird, and the Outlook Addon App for Thunderbird. I can receive emails to the Office365 account no problem, but cannot Send emails from the Thunderbird (Host) Office365 email, unless I select the Default Outgoing Server which is a different email. I have reset Passwords, related Server settings, and Account Config settings numerous times.

The only other option is to send from the Outlook Addon App ,,, this works fine, But I cannot access the Thunderbird Local Folders from the Outlook Addon.

Any assistance with this issue is truly appreciated. TD

Hi, I would like to install Thunderbird on my computer to connect it to my Wanadoo account. What are the settings: IMAP, ...? I also want to install the folder structure on another drive to avoid loading my system drive. What other things should I be careful about to avoid making mistakes or wrong settings or security ? Eventually, I would also like to add another Gmail account or another provider. Thanks in advance

Not sure where/how to post this, so starting here (and happy to move/amend this posting as appropriate.) 15-Oct-2026

Background: I've got a yahoo ("free") email account for many years, and wish to move the current contents of my Inbox to a folder (on imap, not local). Recently yahoo appears to have moved to "cloud" arrangement internally (not sure, but it appears to be the case.) The problem I'm experiencing (below) I believe may be yahoo's back-end cloud processes getting out of sync with Thunderbird's view of the same activity. Therefore, I'm seeking help on how to accomplish this (=I don't think there is a bug in Thunderbird, rather this is a plea for how to manage yahoo's email service for my account.)

Symptom: Moving large number of emails between folders both hosted on yahoo, peers to my inbox on yahoo, using imap - the "export" imap service). Thunderbird says it completes the task, but many (not all) of the moved emails re-appear in yahoo's inbox after a short time, so this makes moving a large (more than a few hundred) emails a *very* laborious process.

What I'm trying to do: I wish to move my current inbox (has about 7.5K messages) to an IMAP-hosted folder (same account, etc.,yahoo email would see this folder as a peer to inbox). When I select all of the messages on inbox and tell Thunderbird to move these to the local folder, thunderbird appears to indicate the task was completed. If I move a very small number of emails at a time, that does complete successfully (=thunderbird says task completed, and the moved emails do not re-appear in yahoo inbox.)

Thanks for looking at this (long) posting and (particular to moderators) if I've posted this incorrectly or in wrong place, please assist!

Dave

As of Oct 12 2026 I also have this issue. About a week before the 12th I was getting messages that I needed to sign into my RCN account which I would do and it just kept asking me. A few times each night to start then right before it shut me out I had over 50 of these messages just flooding my screen. I never did get a screen shot of that message, but did for the 2 error messages I got later once it shut me out. I shut down my computer the night of the 11th then when I signed back in on the 12th I could not send or recieve any emails. SOmething similar had happened before, but when I shut down again it went away. This time it did not. I then tried to access my emails thru the webmail I can access, but that also had shut me out. I also tried my tablet, a borrowed smart phone, but I could not access anything for my emails. I troubleshooted with my email company and my internet company, but they found nothing. Then I shut off the wi-fi on the smart phone and bin go I could access the webmail. But I still cannot find anything on what to do to fix this. I use RCN for my email, Spectrum for my internet. It is a POP3. Running Thunderbird version 153.5 Oesr (32 bit) Meadow, which says it is up to date. I have norton 360 anti virus & do not use VPN. I disabled my Auto-protect and firewall on the Norton and that did not change anything. I have sent the error messages to RCN and also troubleshot with Microsoft and had some hints, but nothing has come of that yet. Here are the screen shots of the only 2 things I ould capture. The error message was when I was trying to access my email thru Thunderbird. And it came up every time I tried to send messages, not that does not show up anymore and nothing happens when I try and send anything. The second one was when I was trying to access the RCN webmail and it would not let me in on anything I used. Until I shout off the WI-Fi. Then the smart phone could access my webmail account.

I use Thunderbird with a info@... account hosted by TransIP.

When I send an email, especially when I reply to a previous email and even more when this was my own email, the sent email is not always saved in the Sent folder: neither in the webmail of TransIP nor in Thunderbird. It seems random when emails are and are not saved in the Sent folder.

The replies are sent through; the recipient receives them.

What can I do?

Despite my attempts to find an error in my outbound mail settings, I keep getting the message below.

The test of the connection to the server passes everytime, but the mail form will not allow mail to be sent.

It's the ESR version. It all started when I added a vcard to my outbound mail.

"Sending of the message failed. An error occurred while sending mail. The mail server responded: Sender refused. Please verify that your email address is correct in your account settings and try again."

When i send an email , it goes to the destination email address all right, but the problem is that it creates two identical entries in my local "sent" folder. As if i had sent the email msg two times. This happens only with my hotmail.com account. All of my other accounts (gmail, yahoo etc) dont have this problem. I am using a windows 11 laptop, and both my windows and Tunderbird are fully updated.

Using Thunderbird 115.18.0esr Supernova 64-bit on Mac laptop OS 10.13.6. Worked fine for years, with ongoing Thunderbird updates, even though Mac OS is 32-bit. Suddenly, after 10/6/26 can't retrieve emails although I can see them on the ATT Yahoo server website. Can still send emails with Thunderbird. Inbound server settings are: POP server inbound.att.net, Port 995, SSL/TLS, Normal Password (I long ago created a Secure Mail Key, and even tried creating a new one). But inbound server name doesn't show in Saved Passwords (only outbound server with Secure Mail Key as password)? I have tried everything suggested, repaired my inbox folder, updated Thunderbird files, etc. in Profile as recommended. But still no prompt for password when attempting to get messages. Just shows "Done" at bottom left with no new messages received. But new messages are seen on server website. So it appears that Thunderbird isn't able to connect to the ATT Yahoo server to get emails. Why? And what else can I do? I love Thunderbird and want to continue using it.

I have been getting the following error message each time I log into my email today: " The STAT command did not succeed. Error getting message number and sizes. Mail server pop.bluedomino.com responded: [SYS/TEMP] Internal error occurred. Refer to server log for more information. [2026-10-14 12:31:46]" I get a message for each of my email accounts. My spouse also gets the message on hers. The server we use has just been transfered from Blue Domino to Network Solutions.

A week ago my sent emails were being rejected and the error message included something about bluehost (I called them and it was fixed within the day). Now it's happening again and my error message says:

host eig-east.smtp.a.cloudfilter.net [3.228.35.199]

   SMTP error from remote mail server after end of data:
   550 Connection Rejected - see http://www.spamhaus.org/query/ip/162.241.218.139 AUP#BL

I receive emails yo simon@padworks.plus.com, but cannot send them, with a message saying ...

Sending of the message failed. An error occurred while sending mail. The mail server responded: Unknown sender. Please verify that your email address is correct in your account settings and try again.

please also reply to simondowthwaite246@gmail.com

I have used Thunderbird for years and have updated new versions. This past week, I can no longer compose new emails; no prompt given for that function. What can I do? I am not a computer geek, so I don't really know how to fix this problem, which seems to be a software issue. Thank you.

I have not been able to get my emails today from Charter on my desktop. Everything was working fine yesterday but nothing in coming through today. It looks like it might load, message that it is downloading 1 of 26 and then says nothing to download. I look on Charter website and there are current emails to download but Thunderbird must have a glitch. I have been on the phone with Charter twice, all the settings are correct for incoming and outgoing ports.

I have looked at the settings in Thunderbird and they are correct. I can get the emails on my iPad and iPhone with the Thunderbird app but not the desktop.

Can anyone give me some direction of where to check next?

I have 5 Gmail accounts they're all configured the same I automatically let thunderbird install two but none of the other three will connect i have tried everything i can think of but can't get thunderbird to connect to my gmail account . the gmail accounts are all configured the same and i'm using the same thunderbird configuation