Knowledgebase

When cPanel configures a new account a Default email address is also setup with the username of the account.
For security reasons, why you should set your domain's catchall or default POP address as :fail:
Using :fail: the email is never accepted into the server.
During the initial SMTP negotiation when the sender's SMTP (Simple Mail Transfer Protocol) server connects to your SMTP server, the sending SMTP server issues a RCPT command notifying your server which email address the following email is intended for.
Your server then checks whether the recipient email address actually exists on your server (a POP3 account, an alias or a catchall alias) and if it does not, it issues an SMTP DENY which terminates the attempt to deliver the email.
o This saves bandwidth as the email data is never received into the server
o This saves server resources as the email never has to be processed
o This complies with the SMTP RFC's because the sending SMTP server receives the DENY command
o Your server does not send a bounce message (just the DENY command)
o Your server does not send anything to the sender of the email (i.e. the address in the From: line)
o The sending SMTP server is responsible for notifying the original sender

Here is a simple explanation of what happens during the SMTP conversation

* Some other SMTP server connects to your server on port 25 and initiates an SMTP connection (EHLO command)
* The other server then sends a message saying who the message is from (MAIL FROM command)
* The other server then sends a message saying who the message is for (RCPT command)
* At this point your server then checks whether the email address in the RCPT command can actually be delivered on your server. If you do not have a catchall alias configured to point to an email address (Default Address) and you have it set to :fail: the following happens:
* Your server sends back along the same connection to the sending server "Go away, no-one here" (the DENY command)
* The sending server would then normally tell their user that the attempt to email your server failed. Your server does not send a "bounce" message.
As far as your server is concerned, all that has happened is a little SMTP chatter and no email has been received and no bounce sent.

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