If you’re setting up your own fediverse presence at your own domain, don’t make the same mistake I did and call it mastodon.my.domain. Give it a generic name like social.my.domain, activity.my.domain, fedi.my.domain or something similar. You don’t want to tie an endpoint for an open protocol to a single implementation or perpetuate the myth that #Mastodon is the #fediverse.
(Yes, you can migrate to a different subdomain later but it’s not a one-click process.)