If you are referring to how many non delivery responces before the message is sent back to a reciepeints queue, then the answer is determand by your mail service.
For exsample a Microsoft Exchange service can be set with X amount of attempts to resend a message if it is delayed. Most providers set this atribute t none for some codes like 5.1.1 reciepeintnot found. and the message will not be re-sent.
Hope this information was found helpful.
One day E-mails will reach space.
VAR Dynamics is the #1 provider of private-label enterprise class Software as a Service.
Bugzilla
Wiki
Source
Bounce 
Linear Mode
