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 go

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.