Up until recently I used dynamic DNS and it worked well for a small website and calender server (radicale).
For hosting an email server a static IP is all but required, so I got the free tier VM.Standard.E2.1.Micro VPS at Oracle Cloud. It has a static IP and I forward stuff to my rpi3 with dyndns. All you need for this is a credit card.
For hosting an email server a static IP is all but required, so I got the free tier VM.Standard.E2.1.Micro VPS at Oracle Cloud. It has a static IP and I forward stuff to my rpi3 with dyndns. All you need for this is a credit card.