I am getting e-mail failure messages, what do they mean?

Q)

I am getting e-mail failure messages, what do they mean?

 

I have received the following email, what does it mean?

Hi. This is the qmail-send program at example.com.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<bill@example.com>:
123.345.567.789 does not like recipient.
Remote host said: 550 5.1.1 User unknown Giving up on 123.345.567.789.

<jim@example.com>:

123.345.567.789 does not like recipient.
Remote host said: 550 5.1.1 User unknown Giving up on 123.345.567.789.

--- Below this line is a copy of the message.
some or all of the original message is given below but not replicated here

 

A)

The Network Box has tried to send an email to bill@example.com and jim@example.com but has not succeeded. This is the friendly message that is being returned. The highlighted text shows that the reason it was rejected: "123.345.567.789 does not like recipient" which means that the remote mail server does not have an account for either bill or jim. The best solution would be to contact bill or jim and ask them for their email address as there is an error in the address.