Hi!
I’ve installed Yunohost at home on a Raspberry Pi 4 with a noho.st domain. Everything works great so far.
Except one thing: E-Mail.
As my provider has blocked port 25, I’m forced to use a SMTP Relay. So I created an account at mailjet.com and followed this instructions: Configure SMTP relay | Yunohost Documentation
After sending my first testmail, I got a notification from mailjet, that I have to verify my domain:
Note: it might be possible to use an smtp relay which offers an other ports.
If you can’t use smtp relay cause port are blocked an other way could be to use a vpn with a dedicated public ip.
About your question about adding some dns entries in noho.st subdomains, some entries could be forbidden. However it’s possible to try to create a hook custom_dns_rules