Is there a setting to change the amount of time an email will sit in the queue trying to send (in our case to an invalid address) before the user gets the email back from the system saying that it was undeliverable? Right now the default is 5 days as far as I can tell, setting this back to 2 days would make more sense in our environment.
Code:
This is the mail system at host ****.com.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
The mail system 
Bugzilla
Wiki
Source
Mail Queue Timeout Length 
Linear Mode
