Treyedit.com is simple and easy

https://litmus.com/email-testing
&
https://litmus.com/alkaline

Lets set up a call to get the most out of your email efforts.

I started providing email services for my web design customers when I started to build our small agency. We wanted to test the idea of providing those services to our current customers, and at that time I really didn't understand how to code HTML emails, nor did I have the resources to outsource this work as a full campaign or services offering.

I wanted custom templates but couldn't customize the ones from the mailchimps of the world, so I went looking for software that was more or less drag and drop.

I've tried almost everything (on Mac) an found that Direct Mail is the best. DM allows you to easily create HTML emails without touching code. You can test across browsers as well as devices, and they have their own mail server that you can use for delivery / tracking.

Also included are customizable signup forms for your website that will populate your lists & custom DNS options for more branded setups.

DM also comes pre-loaded with lots of templates to get you started & they've provided great support in my experience.

We started using their complete package (software and delivery), then move onto our own setup with SendGrid. We still use DM from time to time, and even for seasoned developers it will be a great tool for your belt.

Check out Direct Mail here: http://directmailmac.com/

I'd be happy to jump on a call and help you to define a best solution for your group at no charge.

https://clarity.fm/justinknechtel/e

I use Notepad ++ on a PC. I'm not sure it is available on a Mac, but if they run Windows on their Mac, then it'd work. It's clean, fast and well done.

Good suggestions and arguments for using a online tool / service here. But if you want to stick within your parameters of a Mac-based solution. Try:

Mail Designer Pro 2 by Equinux:
http://www.equinux.com/us/products/maildesigner2/mail-designer-pro-2/

Free trial and available on the App Store.

Completely wysiwyg, it does previews and customizations for everything from desktop to Apple Watches. And it is particular good if you use MailChimp or Campaign Monitor as you can add their template variables directly; and, there is one-click pushing of your finished email to their respective servers for distribution. You can also output html for other providers; and even PDFs for using elsewhere.

For emails you intend to send directly from Apple Mail itself (if you have a small list) you can use the little sister (the non "Pro" version) of the same program.

I have some minor issues with the program but find that for clients who really can't work with online tools it really steps up to the plate. There is even a "share / lend" via email feature for sending templates that auto install with a click. So I can design a custom template for a client that they can then customize at will.

If you have any follow up questions please DM me and I will be happy to share my VIP call link.

Check out MailChimp or Emma. Both have been very effective with non tech users.

https://clarity.fm/josuesierra/expertise/email-marketing-email-deliverability-best-practices

Recommend using Expressionweb - free to download and shows split screen of html / WYSIWYG

You can edit either side (html code or WYSIWYG) as they are conntected so what you edit on one screen affects the other

Not sure you can use on Mac though :S