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.

Sorry you're dealing with it.Oh, and send the letter with proof of delivery (USPS priority mail letter with proof of delivery is perfect - they don't have to sign for it, and you have proof she got it).Also, make sure you give the proper amount of notice to not renew the lease - in CA if they've been in the unit over a year it's 60 days - just check and do it right.

I'm sure you've tried your best to keep them moving so keep that going and if they stall, serve them their 3 day notice to vacate in their hand, document delivery and then see if that lights a fire under them.  

It's all about word-choice and delivery.

Tesla has not met production of cars that would qualify for this credit yet, but they are likely to at some point during the delivery of this newest model.  

My water company offers a "landlord" bill delivery, and yours may, too.   

I don't know about the notice requirement, but what I did was sent notices via USPS with delivery confirmation.  

I do not know about your area but where I live providing a cluster box is the responsibility of the post office as it is their decision not to make door to door delivery. 

I would just mention mail / fedex/ UPS delivery was asking at  the house for the sister and ask why.