Creating dummy pop account in Outlook 2007 for Exchange 2007.

I have an Exchange 2007 server that is authoritative for two domains.  One user has an email address for both domains ( and are both aliased to his user).  His default address is which is set up using an exchange account set up in Outlook 2007. This user would like to be able to send out of either email address by choice.  I created a dummy pop3 account in his Outlook 2007, but I've run into an issue.

If I set outgoing authorization in the dummy POP account to nothing, he can send a test email to himself through the dummy account just fine.  However, if I try to send an email to anyone else, I get an NDR stating "Unable to relay."  If I try to put in his user account details into the dummy POP account's outgoing authorization, I just get a popup asking for a username and password over and over again, though I am certain the username and password is correct.  I've tried multiple entries for the username including domain\username,, and username.  Does anyone have any ideas on why this is happening?
OAC TechnologyProfessional NerdsAsked:
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Hi DataDudes,

Have you enabled TLS encryption in your client?
Which port are you using for your SMTP 25 or 587?

OAC TechnologyProfessional NerdsAuthor Commented:
I've tried with and without TLS and SSL on the client.  I am using port 25
If you test your connection with Outlook, does the error occure with SMTP or with POP3? Does the test comes with a popup stating the certificate is not trusted or valid?
SMTP in Exchange 2007 requires by default all users to authenticate before beeing able to relay.
Maybe you changed the default security settings on the Receive Connector? If so, try to use port 587

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OAC TechnologyProfessional NerdsAuthor Commented:
I do not get a popup stating the certificate is not trusted or valid.  I've tried using port 587 for outbound smtp, but I still get the popup asking me for my username and password.
OAC TechnologyProfessional NerdsAuthor Commented:
Using port 587 and adding the domain/user with no authentication seems to have done the trick.  Thanks for the help!
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