Searched technet, found that exact question in a newsgroup. Here's what they say:
Subject: 553 sorry, that domain isn't in my list of allowed rcpt hosts
Q: We have a mail server located at ISP. Clients using W98 and configured as firewall client can receive mails from the ISP mail server but can not send any mail out except our own mail adress.
Each time we send a mail, there is an error message "Because server deny one of the receipt, cannot send mail. The mail address denied is XXX@XXX.XXX. subject" ",account:" our ISP's mail server", server:" our ISP's mail server", protocol: smtp, server echo: '553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)', port: 25, security(SSL): no, server error: 553, error number: 0x800CCC79"
What should I do to make the mail server can send all mails out without any limitation? BTW, I had configured smtp filter to allow transferation in ip filter.
A: Its an ISP problem. They have not allowed your IP range to relay through their server. Contact them. I believe that error message is from a QMail server.
Jon
Good luck!