Thunderbird isn't blocking; it just is in the middle as your agent. This problem is happening due to a misconfiguration (beyond my ability to diagnose). For my own PC, when I rightclick a file and send to Thunderbird, Thunderbird starts, but not in write window and with no attachment, so I'm not sure what should really happen,

This has just started happening recently and is occurring on two computers here. Reinstalling didn't help.

This has just started happening recently and is occurring on two computers here. Reinstalling didn't help.

It should not help anything as it is more than unlikely there is an issue with Thunderbird beyond how your account is set up by you.

I would have a close look at what outgoing servers are setup in outgoing servers (SMTP) in account settings. Most folk what see issues differing between what in their account in Thunderbird does and using the operating system to send an email using the default account have two entries in their outgoing servers.

One entry that is used because it is the one associated with their identify in the incoming account and another that is marked default that only gets used when they are not already in a mail account, like when the application is getting launched to send an email with the file attached.

Thunderbird is set as the default email program. Where would I look for any settings except within Thunderbird at Server Settings?

hrsweet3 said

I would have a close look at what outgoing servers are setup in outgoing servers (SMTP) in account settings.

If you can't find account settings on the application menu under the toolbar icon ≡. I really can not help you.

I have been working at outgoing server in account settings in Thunderbird.

Here is what is shows: server name: localhost port: 7363 connection security: STARTTLS authentication method: normal password username: hrsweet3

Also, if I start with the file > send to mail recipient > Thunderbird, and then remove the attached file, the message is sent.

For us to better investigate this issue, we will need some more information because localhost is not something that should normally appear in any server name for mail (except you are using proton mail and if you are using that anything is possible. Really, as it has it's own mail server like software on your computer and uses it for it's rather odd encryption.

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.

https://pastebin.mozilla.org/YLjZ71X7

Any luck? (time frame set for nr 2 above has expired.)

To be honest I have been busy planting a crop and have had little of no time to look at anything at home until this week. So if I did get to look, I have forgotten what I saw.

What I do know is sending mail via localhost is almost certainly not normal. Usually we include a mail server name provided by the mail hosting company. Some folks that pay for encrypted mail with proton mail do so, and use a rather odd local implementation of a mail server installed on localhost. But for proton customers issues appear to about that go away if they don't use proton.