Medical Majijuana transport

[killerweed420]

Thanks for your reply
But I found companies like this, who, apparently, deliver legaly in California state...
Let It Grow Collective
so what is the law saying in their specific case?

If they're using the USPS then its clearly illegal because USPS is federal entity. You could make an arguement that using DHL,FedEx or UPS is legal as long as you don't cross the state line.
Generally if the USPS runs across illegal substances it confiscates them and refers it to the DEA to see if they're interested in following up.
If caution is used cannabis can't be sent through the mail. But just like seeds you risk losing the product.