The Thunderbird add-on that lets you compose directly in HTML is fun for this kind of thing. You can also abuse those signature-maker site HTML signatures into full emails, tightly composed.

I also think PDF newsletters are cool if you're doing anything people might like to store. I have been trialing Textmaker 2018 for this in Linux and it will do most desktop publishing stuff like linked text frames really easily, plus export to HTML, pdf, and epub.

I use mailchimp but probably could get away with plain old email (I have about 45 subscribers). I just use the HTML editor that mailchimp provides and write some inline CSS. It's all "handcrafted" which is what I want. Hope this helps :)

I will say that their free tier (I think it's 10k emails per month?) is way more than enough for my use case. I'm not affiliated with mailchimp.