Gmail S/MIME Encryption

If like me, you use Gmail and send encrypted emails, you will notice at some point that the Gmail interface doesn’t provide support for S/MIME encryption. This doesn’t mean that you can’t send and receive encrypted emails using Gmail; you need to use a different tool to encrypt and read the emails. I won’t go into detail how S/MIME works; there are lots of other websites that provide the details.

In a very simplified nutshell, the key thing to remember is that S/MIME involves sending an ‘encrypted attachment’ called ‘smime.p7m’. You can send this attachment over SMTP and receive it via POP3/IMAP4. When receiving the email, as long as your email client can recognize that there is an attachment ‘smime.p7m’, it will open and decrypt it automatically. (Assuming you have the right certificates installed!)

For instance, Microsoft Outlook has recognized that I have received an encrypted email via Gmail, shown below. I sent this encrypted email from one Gmail account via SMTP and received it in a different Gmail account via IMAP4.