User not local or invalid address – Relay denied in Outlook

User not local or invalid address – Relay denied in Outlook

SMTP Error 551 : If neither the sending mail address nor the recipient’s address are locally hosted by the server, then the ISP’s servers may refuse to relay the message on. Some ISPs implement this restriction to thwart spammers. In our view, here at AnswersThatWork, this is a lazy and incompetent method of fighting spam as most of the time it does nothing but inconvenience no-one other than the ISP’s vast majority of considerate and law abiding users. In our experience this usually goes hand in hand with barely competent technical support. At the time of writing, 14-Sep-2008, a typical culprit for this is BT, British Telecom, in the UK. The way in which it manifests itself is as follows : you have a domain that is hosted by but your ISP is you try to send emails from your domain to


Neither your domain nor Yahoo.usa are hosted by DodgyISP.com, as a result your email is not accepted by DodgyISP’s mail servers and your mail server is returned an SMTP Error 551. To correct the problem you have to call DodgyISP.com and ask them to enter your domain name as an allowed sender.
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