gmail (and other services) users can recieve PGP encrypted mail, if they use a mail client that supports this. And the sender knows whether that recipient can recieve it beforehand, because the sender needs their puplic key to send them an encrypted mail.
if the recipient opens that encrypted mail in a client that does not support PGP, they cannot read the mail body and attachments, neither can the mail provider.
the provider can deliver the encrypted mail they can’t decrypt, because the mail headers (address etc) are not encrypted. the provider only learns what they need to know to deliver it.
gmail (and other services) users can recieve PGP encrypted mail, if they use a mail client that supports this. And the sender knows whether that recipient can recieve it beforehand, because the sender needs their puplic key to send them an encrypted mail.
if the recipient opens that encrypted mail in a client that does not support PGP, they cannot read the mail body and attachments, neither can the mail provider.
the provider can deliver the encrypted mail they can’t decrypt, because the mail headers (address etc) are not encrypted. the provider only learns what they need to know to deliver it.