Suddenly can't send emails

I have been using eM Client free email software for several years and it has suddenly stopped being able to send emails or reply to email.I did go in to checking the settings but I am afraid I didn’t understand what might be missing or wrong so didn’t touch anything. I am an 81 year old non techy. I can go into my TalkTalk mail account and send anything so what do I need to do please. This is the message I get. Not sure but I think this has only started since I installed the latest update a few days ago. Any simple advice welcome.

***** The authentication failed due to the following reason:

“Unexpected end of stream”

(SMTP) An attempt to connect to ***** failed: This could be caused by temporary server unavailability or incorrect settings. Do you want to check the settings?

A common cause is the anti-virus/firewall application and Avast is a major culprit.

Can you try disable them completely, and then send again from eM Client.

If that works, you will need to configure the applications to allow eM Client.

Disabled security, no difference, still will not send or reply email. Thanks for the suggestion, at least I understood that

Did you found out what was the issue?