How has email marketing layout changed over the years?

Question

Layout of letters

Hello. Getting acquainted with the layout of email letters, I come across a variety of tips, but as a rule these tips are for 2015-16 and less often for 2017, not to mention 2018. I am interested to know how things are with the key points in the layout of email letters in order to understand the picture what is happening as of 2018: what works and what doesn't.
So:

1. div - is it possible or not?
   
2. Is it possible to use media queries?
   
3. Online or not?
   
4. doctype, head and body - to use or not?
   

Maybe I missed something important...

Answer 1

1. div - you can, but as always there are nuances
2. media queries are possible, but they do not work everywhere
3. you still need to inline for some clients
4. use

Answer 2

as usual, tables
to send div need to be tricky