Unlike all emails which are sent one on one, The emails which are triggered to end customers from the source application does not require capturing of bounce copies. It is good as long as bounce reports are updated under the reporting dashboard for the information of the customer who is sending the email. 

The custom envelope configuration on Pepipost is used for 2 main purposes which are as given below,

1. It is used to track the email bounces generated during the email sending process for your Pepipost account.

2.  It is also used to replace the original links within HTML content with a unique tracking links so as to track the user activities post email delivery against the emails. These activities like Opened, clicked, unsubscribe, Report spam..etc