Receiving, but cannot send emails

As of today, I suddenly cannot send emails from eM Client.  However, if I access my email account via the internet, I can send emails.  What is the problem?

It might be that your antivirus or firewall is blocking the port or application. Disable your antivirus and firewall and try again.

If that doesn’t work, please provide the error you are receiving.

Why would that suddenly happen?  They have not been blocking it up until now.
I did get an error message to start with, but I am not getting one now - the email is just sitting in the outbox.

Did you disable your antivirus and firewall?

it’s ok now.  I just got another error message that also had a connect button - and it is now reconnected,  thanks anyway