Thunderbird emails

I can receive emails but cannot send them although it worked for a little while after an update. Here`s the message which appeared Sending of the message failed.The message could not be sent because connecting to Outgoing server (SMTP) relay.force9.net 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 have checked and everything is ok