Trusted email: Digital signature with Gmail (IE)

Gmail doesn't have built-in support for encrypting and signing the emails, so there are others options you could try:

Note: There is an ongoing project for a Chrome extension named "End-to-End" which provides encryption, decryption and digital signature. It is not open for general use yet.

1. Use add-ons for Google Chrome i.e. EnigmaGPG, Mymail-crypt etc.

2. You can use PGP (Pretty Good Privacy). It works on public-key cryptography. First you have to generate a public-private key pair via GPG (so that others would be able to send you encrypted messages). You can sign the messages manually and make it armoured to send (provided that you have your recipient's correspondent public key to cipher) or in Mac OS use the gpgtools which contains everything to secure your communication.

3. There are email clients like Thunderbird which has the support for PGP via enigmail or openPGP.

Visit this site for the "End-to-End Chrome" extension.