The contents of this email include the undeliverable constituent email address, and merge tags or placeholders for the donation information. 
Examples of merge tags are:
##ACCOUNTHOLDER##
##AMOUNT##
##TRANSACTIONDATE##

To resolve an undelivered receipt we can run a transaction search for the amount and date of the transaction to resend the acknowledgement. We may need to search constituent records in the donor software for alternative contact information. Please see How to resend a MobilePay receipt.