Although Runbox always tries to encrypt your email during transfer between you and our servers, and between our servers and other email providers, the only way to truly ensure that your email can’t be read by anyone you don’t intend it to be read by is to use end-to-end encryption. This ensures that messages never leave your computer in a readable form, and are never stored on your computer in a readable form.

End-to-end encryption ensures that only you and your intended recipients can read the content of messages.

There are two popular methods for encrypting email this way; PGP and S/MIME. In the table below we show some examples of ways you can send encrypted email with your Runbox account.

Email Client/Interface Operating Systems Encryption Type
Runbox Mail Manager All (browser based) With browser plugins installed. Mailvelope, Gpg4win and GPGTools can provide basic PGP/Inline encryption of text in some browsers. Attachments are not encrypted.
Thunderbird Windows, OS X, Linux S/MIME, PGP with Enigmail add-on.
Apple Mail OS X S/MIME, PGP with GPGMail add-on (as of release 2018.4 GPGMail is no longer free software).
Microsoft Outlook Windows, OS X S/MIME.
Windows Live Mail Windows S/MIME.
iPhone/iPad Mail iOS S/MIME.
also MailDroid Pro
Android S/MIME and PGP with Crypto plugin.
K-9 Mail Android PGP with APG installed.


PGP and S/MIME both work in similar ways, but there are some differences between the two that are important to note.

  • Widest native support amongst email clients
  • Based on chain of trust, i.e. you trust the certificate authorities
  • Certificates can provide robust independent identity verification depending on the type purchased
  • Requires a purchased certificate to work reliably
  • Self-signed certificates can be rejected by some email clients
  • Supported by a smaller number of popular email clients
  • Based on web of trust, i.e. you trust the public encryption key belongs to the supposed owner
  • No set up costs
  • A number of free open source tools are available
  • Self-generated keys give you complete control, but are not necessarily independently verified

Note: Runbox currently provides help and support for PGP when used with the email clients and webmail systems outlined in the table above.

Setting up OpenPGP Encryption

Using freely available software that offers encryption based on the OpenPGP standard (PGP stands for Pretty Good Privacy), you can begin securing your email against unauthorised access.