when dealing with email, the necessary steps should be implemented by
your email application (aka mail user agent (MUA)).
Technically this is done it two steps, so the signature stays there
and can be verified even without encryption.
What MUA are you talking about?
Best Regards,
Bernhard
ps.: Flattr Gpg4win at https://flattr.com/thing/2053326,
if you appreciate this answer and my work within the Gpg4win Initiative.
This will be a feature of the “MIME Support” we are currently working on for gpgol.
Then you can just select “sign, encrypt” and when you send the message the complete message with attachments will be signed and encrypted in a standard format.