Errors such as this often occur when the sending email address does not match the SMTP server email address or when there is no authentication on the SMTP server.

Thank you David. But this problem does not occur on my office PC using the same settings. Furthermore, I have already tried countless sending email addresses and they all result in the same problem.

I understand little about the subject and the problem seems quite challenging to me.

Another thing: Whenever I open TB it starts with the same message of an error that happened more than 3 months ago (Attached).

It may help to post screenshots of the account pane and the SMTP server pane for both accounts. You also seem to have multiple accounts. It may help to verify that all accounts are linked to their appropriate SMTP servers, as that is a common problem seen here.

I don't know if I'll be able to send screenshots from my work computer as I'm going on vacation tomorrow. I send here screenshots of all the accounts I have on my home computer. I have 5 accounts installed and in one of them I can send messages normally. This account from which I can send messages has the server "mail.lonasxxl.pt" and all accounts that I cannot send messages from have the server "mail.oedim.pt".

Ok, It seems you need five SMTP servers set up. Are there? I suggest checking account pane, the one that shows SMTP server on bottom line. This is not the 'server settings', but the account pane itself. There is a possibility that, with four accounts for that server, that they may not be all pointing to their appropriate SMTP server (a common problem). You also have different settings on the servers. Is the account for ssetuplux still on Thunderbird?

Ok, I'll look at the SMTP server in the control panel.

Yes. There are 5 SMTP servers. Sending emails doesn´t work in any of them. I changed the ports on some of them to see if they worked but they didn't.

Setuplux is the email of a customer to whom I tried to send a message and had this same error. This was 3 months ago and whenever I start TB it shows this message.

One question: Could reinstalling TB from scratch help?

Check the account panes to see if each SMTP server is set to the right account. The bottom line of the account pane lists the name of the associated SMTP server. Check your account folders to see if the setuplux is stuck in there. You might also log onto web account to see if the message is in there. Do you receive the exact same error message regardless of which account you try? That is the reference to the egon email address?

Reinstalling rarely fixes errors and sometimes causes more.

Now I´m getting new error message on all accounts. I hope this message is better than the previous one.

"Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) smtp.oedim.com failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) settings are correct and try again."

I'm going on vacation now but I'll have my PC there and I can do more testing. I still have an account that sends messages without any problems (pedidos@lonasxxl.pt), and for now, I'm going to keep using this one. It's my vacation but I'll need to work anyway.

For now, I really appreciate all your help David. It's impressive to see a person so committed to helping others. Thank you very much!!!

And now the error message citing the setuplux email has disappeared when starting TB. I believe we are evolving.

Ok, enjoy vacation. When you return, some simple checks: - check that each account is using the right server. That's fundamental and the cause of many problems seen here. The attached screenshots are example. - compare carefully with the office settings. Minor differences can cause that error message.