14 day notice - how to deliver

[Kosh Vokter]

I sent 14-day pay or vacate notice through certified mail. I also have proof of the notice being delivered to the tenant. I also e-mailed the notice to the tenant via e-mail. I didn't have it deliver it myself or post it on the premise, and so don't have proof of that. 

Tenants have not responded or acknowledged to e-mail or for the USPS mail delivery of the notice. 

Is certified e-mail considered as an acceptable form of delivering the notice or could the tenants possibly claim that they never received any (e-mail or USPS mail)? 

[Nathan Gesner]

Quote from @Kosh Vokter:

You sent it certified and have proof it was delivered. That's all you need. If you feel like hounding the tenant a little more, you can post it to their front door and take a picture for evidence, then drive back to see if it's been removed.