Client needs a templated email
I have a client that was using Fastmail.com, but recently started using me for their website and email to reduce overhead costs.
They want to be able to utilize email templates so they can start a new email using a templated format.
They used this pretty heavily in fastmail.
Do they want the email to be integrated with whatever existing service(s) they have with you, like a WP site? Otherwise, it looks like the only email app on Cloudron is Listmonk. Here is a link for their templating: https://listmonk.app/docs/templating/.
If you want something "better"... I use Sendy.co on a LAMP app in Cloudron, which requires a separate AWS SES setup, but Sendy is super handy for tracking mailing lists AND is simple to create or edit an HTML email template and paste the code into the message.
I think Mautic also does email, but I never stuck with it long enough to figure it all out.
Another far-out option might be Ghost, the blog app, which has pivoted to become both a blog app AND a membership app which basically means emailing lists.