Unable to Send Mail: No Such User Here Error

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Unable to Send Mail: No Such User Here Error

When trying to send an email, you may receive an error message similar to the following:

Your message did not reach some or all of the intended recipients.
Subject:    Test 2
Sent:   3/15/2010 6:23 AM
The following recipient(s) could not be reached:
'test@gmail.com' on 3/15/2010 6:23 AM 550
No such user here

When processing email, a mail server has two types of mail messages it deals with:
  • Unauthenticated Email is inbound email that comes from the internet and can only be destined for a mailbox that lives on the mail server.  Generally, the sender of unauthenticated email is hosted on an external mail server, however, the recipient of the email is always hosted on one of our email servers.  Unauthenticated email is email that is incoming to one of our customers.
  • Authenticated Email is email that is outbound from one of our customers to someone else on the internet who is generally not hosted with us. This is known as outgoing email. When you receive the "No Such User Here" error, this means that you are attempting to send outgoing email, however, you have not properly configured your mail client for authentication.
In your mail client settings, there will be an option that reads similar to "My outgoing SMTP Server requires Authentication".  This setting must be selected in order to send email from our servers to the outside world.

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