Emails returned as undeliverable

When attempting to send e-mail though Outlook, I am receving this undeliverable message:  "The following recipient could not be reached. 550 You must check your mail from this IP or SMTP Auth before sending to..."

This happens with all e-mails except to those within my own organization.

Thanks!
Steve_BradyAsked:
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war1Commented:
Greetings, Steve_Brady!

Are you allowed to send emails outside your organization?  There may be a group policy blocking the sending of emails.  Check swith your IT Administrator.

Cheers!
Steve_BradyAuthor Commented:
We are allowed.  I was sending e-mails fine until recently, when I turned the send/receive settings off because I wanted to log into my e-mail account from another location.  It is when I started sending/receiving from Outlook again that I experienced this problem.  
war1Commented:
What email service is this?  Your administrator may be blocking the default SMTP port. Try alternate port 26 or 587.
zolcerManaging DirectorCommented:
I believe what's going on is this:
Your ISP requires a POP3 login *before* it will accept (and, thus, relay) your outgoing messages. It's called "POP before SMTP", and it's a means of indirect SMTP authentication. Once your ISP knows who you are, he will accept mail from your current IP address for the next couple of minutes.

Look for a check box saying, "Log on to incoming mail server before sending mail ("More Settings ..." in Outlook 2003) or anything similar in other e-mail clients.

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zolcerManaging DirectorCommented:
oh, I forgot ... I'm sure your ISP will let you do SMTP authentication, too. The error message you quoted ("... You must ... SMTP Auth ...") suggests that. Ask your ISP what exactly he requires. He'll most probably have a step-by-step guide.
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