Returned Undeliverable
The Returned Mail: Undeliverable or User Unknown errors occur for a variety of reasons:
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The e-mail address is not valid. E-mail addresses are made up of the username and the POP server to which the e-mail will be sent (for example, username@popserver.com). The username must be a valid username on an existing POP server. Verify that the username and server are spelled correctly. The username and POP server should be separated by the @ symbol. Make sure that a period is in the POP server (for example, popserver.com).
- The e-mail and the attachment are too large. This error can occur when you are sending e-mail with attachments (pictures, sound files, or other documents) that are larger than the destination POP server will allow. The standard limit most e-mail servers will accept is 2 megabytes (2 MB). If the e-mail you send exceeds the limit allowed by the server to which you are sending it, then your mail will be rejected as undeliverable.
- The e-mail is infected with a virus. If your computer has a virus and your system is sending the virus attached to the e-mail, the receiving server may screen and reject it.
- The e-mail is blocked by the POP server because it is viewed as possible spam.