For the past week I have been unable to send emails from T'Bird.
Weds night they admitted at last that they had a problem with Yahoo's servers in USA handling POP3
Sending has nowt to do with POP3; it's SMTP.
Which are you having trouble with, sending, receiving or both?
If it is sending, a spam filter will never be involved.
If it is receiving, a spam filter cannot overcome a password failure.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 19 Meg WBC