What is the standard way, if any, to announce via e-mail that you have a public PGP key and what it is?

I’m making an e-mail system/client. I’m trying to correctly detect incoming e-mails which can be replied to with PGP encryption. This means finding out their public PGP key. I currently do:

  • Parse the e-mail body for a PGP public key block.

I suspect that these could be done:

  • Check for attachments with some kind of standard file name?
  • Check for a special hidden header which either spells out the public PGP key directly, or links to an external resource where it can be fetched?

Thanks in advance for clarifying how one properly detects/sends PGP public keys in e-mail context for maximum support.