Issue Your Own Self-Signed S/MIME Certs with OpenSSL

makeauthority.sh

# Run this once
openssl genrsa -des3 -out ca.key 4096
openssl req -new -x509 -days 365 -key ca.key -out ca.crt

makecert.sh

# Run this for each email account.  The system must install the CA cert and the resulting p12 file in order to be happy.

# Borrowed from http://serverfault.com/questions/103263/can-i-create-my-own-s-mime-certificate-for-email-encryption

openssl genrsa -des3 -out smime.key 4096
openssl req -new -key smime.key -out smime.csr
openssl x509 -req -days 365 -in smime.csr -CA ca.crt -CAkey ca.key -set_serial 1 -out smime.crt -setalias "Self Signed SMIME" -addtrust emailProtection -addreject clientAuth -addreject serverAuth -trustout
openssl pkcs12 -export -in smime.crt -inkey smime.key -out smime.p12

Thanks so much @sm5050 !!

https://www.dalesandro.net/create-self-signed-smime-certificates/

That was the perfect guide and now I can do a self signed S/MIME cert on my Mail.app on macOS 10.14.3.

I have step by step follow the post above, and could not encrypt mail with smime.
Generate certificates successful but there is no lock display in the mail receiver.
Could you please describe the steps you've done?

Thanks so much @sm5050 !!

https://www.dalesandro.net/create-self-signed-smime-certificates/

That was the perfect guide and now I can do a self signed S/MIME cert on my Mail.app on macOS 10.14.3.

I’m not able to get Mail on macOS(10.14.4) or Mail on iOS(12.2) to cooperate with me.

I’ve create ca and test user(test@gmail.com for example), install test user’s p12 on my iphone, and Login test user on iOS Mail.

Turn on the settings for sign and encrypt in account/mail/advanced.

Finally, go to mail and send mail to my self. Nothing happend (no lock as describe in many other tutorials), login to webpage and the mail is plain.