---
title: "S/MIME"
canonical_url: "https://www.speedzone.fi/tuki/en/kb/smime/"
post_type: "ht_kb"
published: "2026-05-18T06:39:00+00:00"
modified: "2026-05-25T08:14:43+00:00"
language: "en"
author: "kati"
taxonomies:
  ht_kb_category:
    - name: "Webmail.zone.fi (web based e-mail)"
      url: "https://www.speedzone.fi/tuki/en/kb-categories/zone-webmail-web-based-e-mail/"
    - name: "E-mail"
      url: "https://www.speedzone.fi/tuki/en/kb-categories/e-mail-en/"
---

# S/MIME

S/MIME (Secure/Multipurpose Internet Mail Extensions) is a standard for signing and encrypting e-mails end-to-end. Usually signing, verifying and encrypting/decrypting is done by the mail client.

Using S/MIME with your standalone email client such as Thunderbird, Outlook or Apple Mail is supported.

### S/MIME Support in Webmail

[SpeedZone Webmail](https://auth.webmail.zone.fi/?lang=en) can verify the validity of incoming S/MIME signatures and display the signature status to the user.

Signature validity is verified against the same root certificates as used in Thunderbird.

 Important! SpeedZone Webmail cannot:
• sign emails
• encrypt emails
• decrypt encrypted emails.

S/MIME signing and encryption must be done in a separate email client, such as Thunderbird or Outlook.