I reckon posts linking to your self-hosted videos would work if they had an embedded video – if your instance set the <meta property="og:video ..."\> tags appropriately.

Also possible to make posts on your own instance which automatically federate to lemmy communities, as in this example which originates from a mastodon instance: https://lemmy.ml/post/41288461

https://joinpeertube.org/instances

Peertube is federated and self-hostable.

Even better, posts linking to peertube videos get an embedded video in the post:

“Instructions unclear…”

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• For incoming mail, on your server run a mail retrieval agent like fetchmail to fetch mail from the externally hosted mailbox into a maildir on your server.
• To serve that maildir to your clients, on your server run a mail delivery agent like the IMAP server Dovecot.
• To accept outgoing mail from your clients, on your server run something like Postfix with a relayhost configured with the details of your externally hosted SMTP server.

There’s nothing unusual or tricky about any of this arrangement.