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 (`-mhe=on` enables archive header encryption)

How to send sensitive data by email

What is the main problem

Sending any kind of information via "standard" email, i.e. without end-to-end encryption (E2E), is in general insecure since all mail data can be read by attackers. Consider email as an electronic post card.

/!\ Important: Never send sensitive information in emails (neither in the subject/body nor as an unsecured attachment)

Unfortunately, to setup an E2E email is still challenging for the majority of users and annoying when you just want to send a single email to someone you do not correspond with regularly.

Simple workaround

In case you want to send sensitive data (e.g. credit card, personal data, etc) via email, it is much easier to store all these data in one or more file(s) and send them as an encrypted attachment.

Sending encrypted attachments

  1. If your data are already in a document (e.g. Word, Excel) you are done with this step. For other data just create a new file (e.g. TXT) and enter your data.
  2. Locate the document(s) you would like to send in Windows File Explorer and right-click. Click 7-Zip, then Add to archive... (see image).

    • Remark: 7-Zip is installed on all ISG managed Windows clients. Users of self-managed/BOYD devices can download 7-Zip here.


  3. Within 7-Zip select the archive format and Encryption method as shown in the image. Furthermore enter a password for encryption, according to the following rules:

    • Select a strong password, i.e. [a-z,A-Z,0-9] and at least 10 characters long.
    • The password must be different to any other passwords you use (also to encrypted attachments you sent to other users).
    • Keep in mind that the data in the encrypted archive cannot be recovered without this password.


  4. Create the archive by clicking on OK. If you have not changed the location, the archive will be created in the same location as the original data.

  5. Attach the encrypted and password-protected archive to your email and send it. /!\ Do not send the password with the same email!

  6. The best way to send the password is to use a different communication channel and to send it plain, i.e. without any further information (like the purpose of the password). Here is a list of possible communication channels in decreasing order of their level of trust:
    • in person
    • by phone
    • via chat, WhatsApp, Signal etc.

    • by a separate email

Receiving encrypted attachments

  1. Save the attached encrypted archive to the file system
  2. Locate the archive in Windows File Explorer and right-click. Click 7-Zip, then Extract Here (see image).


  3. Enter the valid password

Additional note for Linux users

7-Zip is also available on our managed Linux clients and for the major Linux distributions (package p7zip). On Ubuntu the default archive tool ark works as well.

  • Encrypting an attachment
      /usr/bin/7z a -t7z -mhe=on -p <archive>.7z <file>

    (-mhe=on enables archive header encryption)

  • Decrypting an attachment
      /usr/bin/7z e <archive>.7z
    Note: 7z will prompt for the password automatically

Email/AttachmentEncryption (last edited 2021-04-22 13:18:05 by mreimers)