When emailing a set of recipients with duplicated e-mail addresses, CiviMail reports that it is sending to each record, but it actually only sends to the de-duped set

When sending a mailing to a set of recipients which contain duplicate e-mail addresses (i.e. the same e-mail address(es) shows up in the recipient list more than once), CiviMail reports that it will send the number of messages that corresponds to the duplicate set (i.e. all records). But then it actually sends to the de-duped set (as though you ran SELECT DISTINCT civicrm_email.email ... to get that list).

The sending behavior is correct, it should de-dupe the recipient e-mail list before sending. But the reporting should be corrected, both in the pre-sending info and in the post-sending report.

For example, if you have a group with 6 records, of which only 4 have unique e-mail addresses, CiviMail will say it's sending to 6 recipients, the sending report will say it sent 6 e-mails, but it does not appear to actually e-mail any of the duplicates more than once. Each unique e-mail address receives one copy of the mailing. Again, that's the correct and desired behavior. The reporting should be fixed.