Multiple -r's:
gpg -e -r recipient1@example.com -r recipient2@example.com
That products some ciphertext which can be decrypted by either recipient.
gpg -e -r recipient1@example.com -r recipient2@example.com
That products some ciphertext which can be decrypted by either recipient.
"encrypt-to YOUR_KEY_ID"
in your gpg.conf
This is especially significant if the recipients have different sized public keys. If you send a message to a 2048-bit key and a 1024-bit key, the message only has 1024 bits of security. So you really do get a weakest link effect.