Beginner questions

After that K9 Mail is back, maybe I will give it a new try. But I have some questions. Maybe someone can give me an actual answer.

Where can I setup to PGP sign mails only, without to encrypt them via PGP? I can’t find such an option.

Another question, when I create a new identity, where can I setup the SMTP server for this identity? I didn’t need to fetch mails under this identity, only send mails via the SMTP of the selected identity.