I liked using priority mail with delivery confirmation, when necessary to have official notice of anything. 

Doesn't cost much for the notice and delivery/posting.  

Cut a deal that you will source with one if they take care of you and handle all the delivery/warranty matters.Many tenants want the service of them so you will rent quicker if you provide the option.  

Something has changed in USPS First Class mail delivery.

(pray that you don't find the body).If Mom had called you on the 14th when she was clearing out the property and gave you ALL the keys I'd be more apt to go along with the STORY but here you are sitting by the mailbox waiting for a delivery from someone that hasn't acted in your favor for over three weeks. 

If you don't have a new address from him, mail it with delivery confirmation to the rental address (his last know address).If he still owes you money after that, then I recently found this collection agency, which I've never used, but in your shoes I would try them out. 

Outline the terms of what is considered late (5:00 pm for hand delivery, postmark for mail).

The delivery guy can just try again.So, I guess you should ask your tenants, really. 

The hand delivery was to soften the blow.I welcome each to resign on a month to month lease, at the new rate, and plan to update each unit as they vacate and raise the rent again.

sect...It's Section 1962(f):(f) If the address provided by the owner does not allow forpersonal delivery, then it shall be conclusively presumed that uponthe mailing of any rent or notice to the owner by the tenant to thename and address provided, the notice or rent is deemed receivable bythe owner on the date posted, if the tenant can show proof ofmailing to the name and address provided by the owner.