There are several errors concerning mail delivery that system administrators may see. The most common are described below.

If you mistype an email address, this will yield a delivery failure message as shown below:

Could not deliver message to the following recipient(s):
Failed Recipient: user@example_domain.com
Reason: Failed to connect to the recipients mail server. No MX records were found for the 'example_domain.com' domain.
Failed all attempts to connect to the recipients mail server.
Attempted to send the message to the following ip's: xxx.xxx.xxx.xxx

Another bounce message that you might see is:

"Failed four Attempts to connect to recipients mail server"
This means the SmarterMail has made four attempts to connect to the remote email server to deliver mail but, a connection could not be established.
If you are sending mail to a user whose mailbox is full you will see this message returned to you:
Could not deliver message to the following recipient(s):
Failed Recipient: user@example_domain.com
Reason: The mailbox is full

If you are sending mail to a user whose domain has exceeded its disk space allocation, you will see this message returned to you:

Could not deliver message to the following recipient(s):
Failed Recipient: user@example_domain.com
Reason: The domain size limit has been exceeded