I have this problem now too as of last week.

I cannot email an invoice from quickbooks with my yahoo email account without going first to yahoo security settings & c/p the long code.  I do NOT have to do it just one time but EVERY time.  What happens when I have to send my annual bulk invoices - 400 of them! - in one day.   I have spoken to Intuit people AND yahoo people.

NO ONE except users understand the problem!!!