An administrator questioned a message a user received:
"A customer sent an email to two users in our company. The client misspelled one of the email addresses. Surprisingly, the user received the message, even though the address was spelt wrong. I looked in Exchange tracking and found 2 emails - the message that was sent to both users with one email address spelt wrong and right after that another email with same subject that was sent to the 2nd user with his correct email address. The user only received one email message - the one with his address spelt wrong. How did this happen?"
This happened because the sender used the Resend option in the NDR they received when the first message bounced. They corrected email address and resent it. This is the message the user received.
The confusion results from the resend behavior - when a message is resent using the Resend button in an NDR, the display address is not updated and the recipient sees the original, incorrect address.
This is not limited to Exchange server email, it can happen with POP3 email as well.