Question : sorry, that domain isn't in my list of allowed rcpthosts #5.7.1  Error

I am getting this error on a few domains that we have always been able to communicate with:

MyMailServer #5.5.0 smtp;553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)>

On one of these domains it was user specific as three peopel from our domain could send without a problem but one or two couldn't they would receive this error all the time.

Any ideas if this is an issue on my server or are they blacklisting my domain or users in some cases?

Thanks for any help.

Answer : sorry, that domain isn't in my list of allowed rcpthosts #5.7.1  Error

Everything needs to match ideally.
MX record,
SMTP banner
DNS
Reverse DNS

If you cannot make it match, then ensure that it resolves correctly to the right IP address.

Simon.