I've had this reported to me multiple times as well....

HCL Notes/Domino 8.5 Forum (includes Notes Traveler)

Subject:

... and in every case, we found the mail in the user's mail file.

In every case, the user either had a junk mail rule, or a different rule enabled in their mail file that moved the mail to a different folder.

Checking with the recipient occasionally came up empty, similar to your experience, but when I opened the user's mail file myself I could find the mail in question.

Not to say that it couldn't be a new issue in 8.5.3, but in all my years as an admin, I've always found the 'missing' mail.

Feedback response number WEBB93RJNF created by ~Sigmund Dworelitnivu on 01/08/2013