problems sending emails via smtp

i have an application 开发者_开发问答that uses SMTP to send emails from an yahoo account. it worked fine one week ago, but now i'm getting this error "An existing connection was forcibly closed by the remote host." (the code is written in ffish but i don't think that's relevant since it worked last week without modifications). what should i do to make it work?

Contact Yahoo. It sounds like php is connecting to the SMTP server correctly, only the SMTP server is refusing your connection, possibly due to the server IP being flagged for spam.