Guys, since I am in "the business", so to speak, I wanted to see what kind of error I got. My ISP is a little more generous with the full error report, which reads:
<<<bertie@batavia.co.za>: host
outbound.mmc1.jhb.tiscalibusiness.co.za[196.28.101.21] said: 550 relay not permitted>>
The problem appears to be with his ISP, or at least one upstream from him, but situated in SA. The SMTP server in question is seeing everything as a relay. Typically, most corporate email servers do not allow message relay because that is what spammers use for their dirty work. Occasionally, a normally reliable SMTP server used by an ISP will generate this message if the software is accidentally set to deny relay. I have seen this happen several times during software upgrades.
Tom, your best bet is to call Bertie on the phone and talk with him and also to discuss the error message above. It is likely that he is unaware of any problems. Your other option is to contact Tiscali, SA, a large ISP in Europe and Africa, and see if they can address the issue. Here is
Tiscali's page. You might be able to contact them as well.