FastMail has excellent documentation to get this set up. Migrating there from GMail (were I already used my own domain) was a breeze.
https://www.lesbonscomptes.com/recoll/pages/index-recoll.htm...
"So, further to recent changes at Gandi, I've just got some more info from support which I've included below. I've purchased domains from Gandi, pre-paying for multiple years of service such that some domains I have don't need renewing until 2027. When I purchased that service the offer was inclusive of 2 mailboxes for the duration of the contract, and now they're planning to remove those inclusive mailboxes and start charging me extra for them from next month.
To me, this sounds like a planned and fully intentional breach of contract."
Sorry, I was not aware that they changed. Currently I don't hold a domain with them. They were always a decent provider. This behavior seems very unfortunate.
Infomaniak also sells email hosting for around 20 Euro per year, they are based in Switzerland. If you have your own domain, just type the domain name as you would buy the domain and if the interface says domain taken, select email hosting (the three dots).