gentiles - Received a check by mistake - should one return it?

Assume a Jew received by mistake a non-Jew's mail containing a check. The Halacha prohibits the return of an Avaidas Akum meaning an object which was lost by a non-Jew, unless it is done to bring out a Kiddush Hashem or for the Jew's benefit.

In this case the non-Jew will never know that a Jew took from his time and deposited it into the non-Jew's mailbox - so there would be no Kiddush Hashem.

On the other hand however, being that the Jew won't cash the check for himself anyhow, which means he won't gain in keeping it, so to just keep it might be Middas Sedom and would not be fulfilling the Halacha of not returning a non-Jew's item.

In addition, if the Jew doesn't forward the check, the non-Jew will likely be able to replace the check anyhow.

So what shall the Jew do? Rip the check or let it arrive at its owner to enjoy?