If every registered Apple developer have a certificate for signing their apps. Is that certificate also good for signing mails? And by this, I also mean if their certificate is backed up by a root authority CA recognized by other operative systems.
If you have a look at a developer certificate in Keychain, you'll see that the root CA is Apple itself. I'm not familiar with mail signature authorities, but I'm guessing that Apple isn't recognized by most of them (and I would also suspect that the developer root CA would be distinct from any other CA they may run).