Cloudmailin for all incoming then a fairly sophisticated parser app I wrote just using expressjs to put things into crm or tickets or forward as needed to the right folks.
A lot of developers love to “build over buy”, but I think HubSpot would be a great solution to this use case. All of the features you want are available under the free tier
You can use GNUs and Emacs to easily automate your emailing solutions without needing to write much at all.
Check out Sendy: https://sendy.co
I’ve used Zapier for a lot of my low-volume email automation needs. You can have your email list on google sheets with dates for triggering a message, have a google doc email template with variables filled by the data in your sheet.
Probably doesn’t scale super well and mildly prone to breaking, but free and straightforward. Also easy to combine with google forms as well.