The pricing would definitely be much easier to understand with a calculator.

However, I have no quarrel with the approach to pricing here. In order for a service like this to succeed with very established incumbents, it needs to differentiate itself enough to carve out its own niche.

Domains could be used for groups, like families or companies that send internal email.

Yep, that's why I specified "end user" and "set aside internal company e-mails".

I never thought about the idea of having a "family domain", it could be a nice idea, though I guess its naming could be a possible venue for in-family disputes?

Rather than having in-family disputes, I've had relatively poor luck giving way vanity email addresses to family members. There's a lack of understanding and interest in how the email address would work in combination with an existing email account.

My name is "Mark Stosberg" and my email is "[email protected]".

Yep, I meant that:

1) my mom won't have an e-mail address with the surname of her first husband (my dad, passed away)

2) my brother-in-law (brother of my wife) surely won't have it

3) my cousins all have different surnames

4) my wife may accept one, but I talk with her every day and when we don't meet or talk via phone we tend to communicate via post-its on the fridge or similar

Sent externally means to a different account or provider. So basically, sending email to yourself or other users using your account is much cheaper. (There's no spam worries there.)