This might be a network problem. My suggestion for now is to have sent messages go to a folder on PC.

That's the problem....it's having problems saving to a folder on the PC. I've not had this problem in the past This happened after an update. Why it would timeout copying to a folder on my PC doesn't make sense. There is a copy on my providers website in the "sent" folder if I want to retrieve it...it just won't save to the PC. I'm not seeing this problem on other family's computers.

I am confused. You state that the message is on sent folder online, so why are you also wanting to save on PC? My inference was that the message was not being saved.

The idea is to see my "sent" messages in Thunderbird...and not have to sign on to my provider account to use its email interface. Otherwise, I would not even need Thunderbird. I could just sign into my provider account and just use their email tool...but I don't want to do that. Bottom line....Thunderbird is having problems saving any "sent" email with an attachment locally on my PC. It just times out....which doesn't make any sense.

Run Windows in safe mode and then see if messages with attachments copy as expected.

Well...it worked flawlessly in safe mode!

Look at your startup apps (bypassed in safe mode). It's probably your antivirus, such as AVG/Avast, that is scanning attachments and timing out. Disable any AV options for mail or add the TB profile folder as an exception/exclusion.

I don't have any Anti virus apps....but I'll look at some of the high impact ones and see if they are interfering somehow....thank you! : )

This has been a problem with Thunderbird for years. I have exactly the same. Not on one laptop but on all laptops. Occasionally it just shows 'copying message to sent folder' forever and when you hit cancel, then you see a retry button but that never ever works.

When inquiring, the common response is 'network errors' or 'configuration this and that' or 'antivirus such and so' because the developers are in denial but the only right solution is just to use Outlook. Outlook never has this problem.

This might be a network problem. My suggestion for now is to have sent messages go to a folder on PC.

This is a recent issue. If I send an email with no images and no attachments, it copies the email into my "sent" folder with no problem. If I send an email with even a small attachment...it sends the email, but "times out" copying the message to the sent folder. I've checked the account/server settings, they are exactly as recommended. I've changed the sent files to "other"...no difference. I deleted and reinstalled Thunderbird...no change. Ideas?

I had the same issue "Copying message to sent folder" but I think I found the solution. I just did a test and I'm not having that issue anymore. Go to : Settings - Apps - Default apps - Search apps "Thunderbird" click on "Thunderbird" - Then for: ".eml" and ".wdseml" choose "Thunderbird".

I had the same issue "Copying message to the sent folder". I think I found the solution. I did a test and now I'm not receiving that message anymore and it's working for me. Go to: Settings - Apps - Default apps - Search apps for "Thunderbird" and click on "Thunderbird - Then for ".eml" and ".wdseml" Set default as "Thunderbird".

I finally solved the issue....and it turned out not to be Thunderbird at all. My Windows Defender firewall was corrupted by allowing the company I work for to have access to my computer for emails and such. When I uninstalled their access software...it left a few "scraps" in the firewall. I uninstalled Windows Defender....restarted my computer...which re-installed a clean version of Windows Defender....all is well! : )

I am inclined to lock this topic as it has degenerated into recommendations that are unlikely to assist anyone, like associating wdseml files with Thunderbird. The product does not perform the association itself because they should never be opened by a user for reference to anything. They are rubbish really dating back to Windows XP and it's brain dead "Windows search" They most certainly do not form part of Thunderbird mail store.

Ideas?

For us to better investigate this issue, we will need information.

Could you please do the following?

1. Open the menu > Help > Troubleshooting Information, then click Copy text to Clipboard.
2. Go to https://pastebin.mozilla.org/, paste the clipboard by right clicking in the large text area, select paste from the menu, change the retention period to expire in 28 days, use the Paste Snippet button to create a page containing your info, then copy the resulting URL (address) of the page created.
3. Open a reply to this post, and paste the URL to your troubleshooting information you just copied.
4. Please also provide results for the following test on your system
   • Does Thunderbird work as expected in Thunderbird troubleshooting mode?
   • Does Thunderbird work as expected with your OS started in safe mode with Networking. Instructions for each operating system: Windows 10/11, Windows 8, Windows 7, OSX

If none of those tests helps, please perform a log of your connection and post the results. https://wiki.mozilla.org/MailNews:Logging

@Robert van Geel You have your own support topic which you appear to have abandoned. As you are not offering to help the original poster, I suggest you return to your own support topic if you wish to continue the support process as your comments here are actually off topic. If you are having issues locating it, the topic can be found here https://support.mozilla.org/en-US/questions/1370638