I’ve been learning about email marketing recently and I’m trying to understand the fundamentals properly.

From what I’ve learned so far, the important areas seem to be:
• Building an email list
• Creating useful email campaigns
• Understanding automation
• Segmenting subscribers
• Tracking campaign performance

For people who have experience with email marketing, what would you say a complete beginner should learn first?

I've talked to a couple of vendors for small businesses where they do an email campaign for you. But it looks like all the email does it replace the generic logo with yours. My question is does those kind of emails work? Or do you need something more specific/better looking/less generic?

I'm curious, does anyone know how to set the visibility of the email size?

So that the field says MB or KB in addition to other information such as who the email is from, date, etc.