Only real alternative is PurelyMail, which is ok for the simplest cases. Beyond that, their "advanced pricing" is unnecessarily complex and FranklyMail seems to be more polished overall.
Other providers want $5/month per account, which is insane if all you need is e-mail.
I found Franklymail by accident. Everything started with a renowned European Webhosting company where I have some personal/family websites and emails running on a classic cPanel hosting. Unfortunately, they increase their prices every year and I saw that at the next yearly renewal in January 27, I'd have to pay 8 times what I paid initially, a few years ago. So, I decided to take a cheap bare metal VPS under Debian Linux and transformed it in a minimalist but powerful web server with Caddy and PHP - everything done on the CLI. Now, I'm moving one website after the other over.
Afterwards, and that's where things become interesting, I looked for a similarly lean and minimalist mailserver to run on the same VPS, but couldn't find one. But I found - guess what - Franklymail! I traded many working hours against $9/year and I'm still amazed. When I'll have moved all mail boxes over to Frankly, I'll have for sure to pay a few cents more for additional storage, but I'm more than ok with that, seen this lean and easy to install (almost click-to-run) mail service. Will also for sure recommend it around me.
Emin, thank you so much for your great work!
The no per-seat pricing is a refreshing approach for email hosting. I upvoted this. Supporting JMAP alongside IMAP and SMTP is also a nice touch for keeping things flexible.