I have been getting this error message with a couple of clients now. It only happens when someone from yahoo wants to send a few of my clients an email from yahoo. My clients can send them an email with no problem. DNS appears to be ok with no other domains being blocked. No blacklists, etc... Let me know if you need more info. This is the Message: Message from yahoo.com. Unable to deliver message to the following address(es). < <mailto:user@xxxxxxxxxx <mailto:user@xxxxxxxxxx> >> user@xxxxxxxxxx <mailto:user@xxxxxxxxxx> >: Sorry, I wasn't able to establish an SMTP connection. (#4.4.1) I'm not going to try again; this message has been in the queue too long.