The ability to provide email services to clients includes two critical functions: SMTP and POP3. Together, they provide the means for sending outgoing mail and receiving incoming mail. SMTP service allows clients to send outgoing email to any valid email address. The SMTP server performs two basic but important functions. First, it verifies that anyone attempting to send outgoing email through the SMTP server has the right to do so. Second, it sends the outgoing mail. If the mail is undeliverable, it routes the message back to the sender.
The SMTP server functions in much the same way as your local Post Office. The sender must have permission to send the outgoing email message. The Post Office requires postage to send a message to the recipient. Nexus requires that you have checked your POP3 account for incoming messages within the last 30 minutes before being allowed to send. Think of checking before sending as buying a stamp at the post office. Once this requirement is met, the mail is sent to the recipient.
Problems can occur in the delivery of email and postal mail. Mail sent to non-existent addresses will be returned �address unknown� or �user unknown�. Just as the Postal Service will return your mail with a message "stamped" on it as to why it was not deliverable; our SMTP server will return undeliverable mail with an indication as to why it was not deliverable. When email "bounces", or is returned to you, it is done so because it was undeliverable for one reason or another.
Finally, you need to configure your email client so that it knows what SMTP server to use for sending messages. In order to send mail through your server, set your outgoing mailserver to mail.example.com (where example.com is your actual domain name).