Summary:
PerfectMail does not seem to be sending reject messages for unknown users. If a recipient is unknown then the sender should get a rejection message.

PerfectMail will always send a Rejection Notification for e-mail addresses that it cannot validate or messages that cannot be delivered to the destination mail server.

If PerfectMail cannot deliver an e-mail or if the recipient address cannot be validated, it will *always* return an SMTP Rejection Message. However, some mail servers may discard or rewrite these rejection messages. This behavior lies with the remote mail server and is beyond the control of PerfectMail.

The only exception for this behavior is when PerfectMail is not configured to "reject unknown addresses" and the back-end mail server is also not configured to "reject unknown addresses". In this case, messages addressed to non-existent e-mail addresses will be passed to the back-end mail server with unknown results.

If both your PerfectMail server and your back-end mail server are not rejecting unknown addresses, you can easily re-mediate this issue by doing one of the following:

1. Enable SMTP Recipient Filtering on your back-end mail server and enable "SMTP Recipient Filtering" for the domain in "Domains=>Domain Admin", or
2. Define an explicit list of acceptable e-mail accounts on your PerfectMail server. Go to the web interface menu "Domains=>Domain Admin", select the appropriate domain, click through to E-mail Address Maintenance, and create an explicit list of e-mail addresses.

After performing one of these tasks, update the settings for the domain in "Domains=>Domain Admin", to "Reject Unknown Addresses".

More on Rejection Messages:

There are two types of rejection messages that can be created in e-mail: SMTP Rejection Notices and Non Delivery Reports (NDRs). PerfectMail uses SMTP Rejection Notices. These rejection notices are exchanged during the SMTP mail exchange; when e-mail is being exchanged between mail servers. Non Delivery Reports (NDRs) (also known as "bounce" messages) are automated rejection messages, created by some mail servers, and returned to the "apparent" sender of an e-mail. NDRs are susceptible to E-mail Backscatter issues and abuse. After a message is received a mail server has no ability to validate the original sender of the e-mail message. Spam messages are often sent with a forged sender addresses (often legitimate e-mail addresses, but not of the actual sender), and the forged sender will receive these NDRs rather than the actual sender.

PerfectMail is able to give notification during the e-mail exchange because it is a Live Filtering Solution. PerfectMail analyzes, filters and responds to e-mail in real time, during the message exchange. This guarantees that PerfectMail sends a rejection notification and that the sending server received it; which is implicitly the correct server to send the notification to.