That process is being initiated by Windows, so I suggest investigating the Windows default settings.

Windows default email is MS outllook. Default pdf is adobe.

What is the link that is invoking Thunderbird?

I have a pdf file open that I have filled in ( from the bank) and I want to send it to the mext person to fill in. When I click 'submit' I expect it to open MS office outlook email ( my default app for email) BUT instead it opens Mozilla Thunderbird.

But my question was what does the submit process invoke? What HTML is being clicked?

A pdf file. it invokes a mail handler ( because the submit option is there to submit the file to either the next person by email or to the bank- by email

Please understand, Thunderbird is subordinate to Windows and cannot override it. Can you forward me a link to the website you are using or in someway let me see the submit link?

https://www.natwest.com/content/dam/natwest_com/currentaccounts/downloads/NWB-Personal-Mandates-SMART-FORM-Live-V1.0.pdf?extcam=R_EMC_0_MTA_AATP_AATP_PBET1

Click 'third party mandate to start, then 'continue' Form there, you can scroll down to 'submit'. You don't have to fill in anything... select 'no' and that is the point at which thunderbird opens. ( instead of outlook)> I suppose, if I actually understood the page that comes up in thunderbird, I could use it to send to a recipient. I tried putting an email address in CC, and thunderbird seems to be sending the file but it just sits there going round and round. Worst case, I could delete thunderbird, but I'd probably never be able te get it back set up using news eternal server :) thanks for your help sofar. Martin

Here is my observation: it appears that Thunderbird is running at the time you click submit button. To verify it, I exited thunderbird and clicked submit - and Thunderbird started, as it is my default. Then, I exited and started a different email program and then clicked submit. And the submit went to the other program. If it is important to use Outlook, I suggest you exit Thunderbird prior to clicking submit button.

Thunderbird isn't running when I click submit ( unless it's running in the back ground unknown to me... ) I can double check later by running task manager just before I click submit. OTOH, my outlook is open all day and certainly when I click submit. Thanks again.

Have you had a look in Thunderbird's settings at the system integration to ensure that Thunderbird is not changing the default each time it starts?

Have you checked the same thing in outlook?

My personal experience was outlook changed the default to outlook every time I opened it. So did Thunderbird, so it changed at what appeared to be random until I worked it out.

You gave me the clue !!! In settings, there is a box that says 'check every time on power up'. It wasn't ticked. So I ticked it. It now sends the pdf file to my draft folder in Gmail. From there, I just send it to my email account Tools/general/system integration/ a tick is in 'always check if TB etc...' Now click on 'check now'.... untick 'use thunderbird as email' Tick ' always perform this check on starting TB' and 'set as default' Hope that helps someone else and you can remember the solution.( Beacause I won't be able to- I'm too old :( )