I’m interested in setting up my own instances for Lemmy, Mastodon, and Matrix.

Can I use the same https://domain.tld for all of them without any subdomains?

For example:
lemmyuser@mydomain.tld
mastodonuser@mydomain.tld
matrixuser@mydomain.tld

Will this work across all of my self-hosted instances, or do I need to append a subdomain for each, e.g., lemmyuser@lemmy.mydomain.tld?