Digging up old thread as its still not resolved (i'm getting this as we getting rate limited now)
The problem is when the ISP disconnected you after accepting the connection (spam checking, rate limiting on from/to address etc).
The send_data command don't check if the $this->_smtp_connect is still active with each sending of the command, so if ISP drops connection in middle of transmitting, then fwrite throw an uncaught error.
I will when I have time again if I can add a check if "$this->_smtp_connect" is still active before trying to send data and catch error from fwrite gracefully. Just bit swamped.
