SMTP 550 5.7.1 Unable to relay for ...

[FRrogoy]

I can't seem to keep the SMTP mail server running. Had it going for a couple of days on 2 PC's - one Win 2k and the other XP professional. Then started getting the Unable to relay message. Got one of them working again by re-doing the IIS setup, but can't get the other going again.
I'm trying to run a web app standalone, using localhost. I expect the mail to be queued until the PC has connectivity again. Running Apache, PHP, MySQL. PHP is doing the sendmail. I don't understand the "relay" function and why it is trying to relay when I'm not connected to the network. (I get the same message when it is connected.) The server instance of the application works fine.

Frank

 

[FRrogoy]

Update: I got it running again. I entered my PC's IP address (correctly!) in the allow relay dialog. That gave me an error saying to check SMTP and PHP.INI settings. I removed the IP address, saying to allow all (the way it was previously). I tried refreshing and restarting SMTP after each change. It started working again after I put it back the way it was originally... I had tried those changes yesterday and it didn't make any difference.

Frank