The number of bounce messages shown in eNotify for a mailing doesn’t always match the number of bounceback emails you receive in your inbox after the mailing.
This is because the bounceback messages you see in eNotify are generated by direct (non-email) messages sent by the receiving email server during the mail delivery transaction between our sending server and the receiving server. eNotify only counts the direct messages from the server during the delivery transaction, not the emails sent to you (the sender), so they're not necessarily tied to the bounceback email messages.
Not all email servers are configured to send bounceback information in the same way. Sometimes a receiving server will both return a direct bounce message during the transaction and send an email notification to the sender's email address afterward. Sometimes it will send only the direct message. Sometimes it sends only the email. Sometimes neither. Receiving servers are not required to communicate anything about bounces or rejections; it is considered merely a courtesy.