Using MS Exchange 2007, I have user account using POP3. When sending messages, error 550 5.7.1 occurs "unable to relay". Question; how do I configure mail server, exchange 2007 to allow this user id (helpdesk@xyz.com) to send mail? When I review the account settings, I am able to successful place a test when clicking on TEST button.

BTW...When using Outlook or Evolution e-mail client configured for POP3 / SMTP, the user account cannot relay or send mail. This applies to using telnet xyz.com 25 as well. "Unable to Relay".Are there ways for me to assign permssions to the user ID. when I look at "get-receiveconnector | fl names,bindings,permissiongroups I see exchange admins, exchange users, anonymous and partners is listed there. someone told me "ExchangeClients" needs to be part of the permission groups. However, there is not a way to add exchangeclients as its not possible to select.Tx.

have you been able to solve your problem? I have similar problem.