No, only by Google.

Email is not controlled by Google. There is myriad of other big players in the field, plus you can get an email server on your own domain up and running in ~ 5 minutes

Email is controlled through gmail in the same way as webdesign is controlled by SEO directed towards google search. People need to access the users on the google platform, and google sets the terms for that.

That is, if you want your email to work you got to play by the rules dictated by google or a very large portion of all email will go away into a black hole.

If Google will start blocking random non-spammy domains from exchanging mail with Gmail users, it not end well for Google and their mail platform.

I imagine that Google is waiting with bated breath for the day when their user base is large enough that they could get away with this, and are sitting, all day every day, with their finger hovering over the button.

It is our role to make sure that they never get sure enough of themselves that they press that button.

e-mail is a communication standard, not a network/system.

You are trying to say it doesn't fit the 'anything decentralised' criteria?

The email standard is the same as only accepting letters mailed using letterhead formatted in Arial font.

When discussing a decentralized version of reddit, it's not the same thing. Protocols are not the same as networks/systems.

That's nonsense. Anything decentralised uses a certain set of rules how independent entities interact with each other. Such rules form a protocol. For example, XMPP is one such protocol. One can build reddit-like or Facebook-like service using xmpp, which will work across multiple independent servers. (In fact, that's what we are going to do, unless we run out of funds first)