What do you mean? Public keys don't usually include an email address. They have an id that's usually in the form "user@host" but that's unlikely to be a valid email address. Maybe some systems use an email address there, but none of those I know.
A valid email address isn't the same as an email address that actually has an inbox behind it. Some of my ssh keys have an fqdn but there's no mx record configured for it. I used to use my bare domain, which does have an mx record, but I've never used real mailbox names for the ssh keys.
