I use mailchimp for a newsletter for my own SaaS site. It is a nice service, they really do make it easy to send and design a mail. Their editor is good, their HTML-plaintext conversion works reasonably well.
What I do not like is the workflow. It's like my usecase is completely unsupported, and I do not understand which usecase they do support. Every time you send a mail you start from scratch: They make you start a new campaign(?), pick again a template, fill in the from address, write a text by editing the template. The workflow does not at all support the thinking that all I do is send a new issue to the same ML like always, which should of course use the same template and infos as always as starting point, where the main thing to do is to change the text in the mail.
I guess they support some marketers definition of how things work there? But really feels strange, as if the text of the mail is an afterthought.
https://kb.mailchimp.com/campaigns/ways-to-build/replicate-a...
My specific problem: I fiddled with the "merge fields" (basically handlebars regex-replace tool) and somehow this broke my email template, but only after I had tested it once and it worked properly. When I copied the original (working) "campaign" and re-sent it, all the text of the email was gone. I copied it and fixed the merge fields, then all the images were gone. After reimporting the images it finally worked.
The really frightening part was that it worked the first time but somehow the act of copying the working email with weird merge fields broke a bunch of other things. So I suppose the copying was imperfect and created a problem with their regex-replace logic the second time. Very glad I tested it a second time before sending it out, overall it took me 6 tries to get it working properly.
I'm on the free tier, and customer support is a paid feature, so I had to figure this out myself.