I used noip.com for like 30 or 60 days. Then I got really annoyed at having to renew the DDNS every 30 days.
After switching to duckdns.org I haven't had any problems whatsoever. It's completely free and you don't have to renew anything manually. You obliviously still need to have a script running to update the DDNS though, otherwise it wouldn't be very dynamic would it.
My mail lived on an Intel atom based mini itx machine for years. I wanted to play with breakup by replication and bought a cheap shell. Now the cheap shell is my only mail server
See email is one of the few things I don't host. I host a webmail frontend, and use my domain. But PurelyMail is an amazing service that's so cheap it's basically free at personal scale with very few limits. I didn't really care to try and deal with having all my mail sent to spam.
I just use stalwart - mail, it's just one docker container, has bleeding edge functions like jmap and there is no need of deeper knowledge. I refer my domain on the settings and got a list of all needed dns-records.
It takes 2-4 days to get SSL and dmarc answers from the big mail-players and if there is nothing wrong with your IP or your records then there is no mail going into spam of someone else.