MeSign

It is a good option to keep your Privacy and stop sending Clear Text Mail Anymore. Encrypt all your mailboxes in one place.

MeSign is a free email client APP with email certificate automation. Once you log in to your email account with MeSign App, the forever free S/MIME certificates will be issued, installed and configured automatically.

Currently, it supports Windows, Android, and iOS. All users' email data is stored encrypted on their email server only (MeSign doesn't hold users' data). So there is no limitation of email storage if the user uses MeSign App to encrypt their emails. MeSign has anti-virus features to scan every encrypted email before the user sees the emails, to make sure all the URLs and attachments are secure when users see them.