Whether you’re using Outlook for Microsoft 365, Outlook on the web, or the new Outlook for Windows, secure, encrypted email messages are essential for compliance and peace of mind. Sending an encrypted message is one of the most effective ways to protect sensitive data from unauthorized access.
In this guide, we’ll show you two easy ways to send encrypted messages in Microsoft Outlook using an Outlook add-in called SendGuard—one of the best email encryption solutions used by businesses worldwide.
What is Email Encryption in Outlook?
Email encryption conceals the contents of your email message so that only the intended recipient can read it. This protects confidential information and helps meet compliance requirements for privacy laws such as GDPR, HIPAA, or PCI DSS.
Are Outlook Emails Encrypted by Default?
No. Encryption is not enabled unless it is specifically configured in Outlook security settings or via an encryption option, such as Microsoft Purview or S/MIME.
How Outlook Encryption Works
Outlook supports email message encryption using a public key/private key system. When encryption is configured—for example, using Microsoft Purview or S/MIME—your public key allows others to send encrypted messages to you, while your private key is used to decrypt them.
Most modern email clients handle this encryption and decryption process automatically once encryption has been enabled in your account.
Note: If encryption options are missing from your Outlook ribbon, contact your IT team to confirm your account settings.
Comparing Outlook’s Native Encryption vs SendGuard
The table below compares Outlook’s built-in encryption features with the added protection offered by SendGuard.
| Feature | Native Outlook | With SendGuard |
| Manual checkbox to encrypt | Yes | Yes (with prompt) |
| Auto-trigger based on content | No | Yes |
| Custom keyword injection | No | Yes |
| Admin-level control | Limited | Full |
While Outlook provides basic encryption tools, SendGuard adds automation, user prompts, and integration with your existing security policies—making it ideal for businesses needing extra compliance assurance.
How to Encrypt Email Messages Using SendGuard
SendGuard doesn’t perform encryption itself—instead, it triggers it by inserting a keyword or X-Header into the message that your existing email encryption software for Outlook (e.g., Microsoft 365) can detect.
This enables organizations to integrate encryption into their workflow without relying on easily overlooked checkboxes in the Outlook ribbon.
Once triggered, your existing platform handles the encryption. For recipients outside Microsoft 365 or Outlook, most enterprise-grade solutions will deliver a secure link that lets them verify their identity and view the message in their browser.
1. Manually Encrypt Emails
SendGuard provides two ways to trigger encryption—manually or automatically—using your existing encryption configuration:
When users go to send a message, SendGuard prompts them via a SendConfirm screen to confirm whether they should encrypt the email message.
To enable this manual encryption option, registry settings must be modified.
Administrators can deploy this configuration centrally across Outlook environments.
Note: We strongly recommend against editing the registry yourself. If you’re an existing customer, contact your account manager or email sales@standss.com to request the Administrator’s Guide.
Registry Configuration Overview
The registry key to update is _EncryptEmailAction, which determines where the encryption trigger will be inserted—before the subject line, after it, or as an X-Header. A keyword (such as “Encrypt”) is entered.
Note: Use a keyword that Outlook encryption software recognizes. Your IT team can confirm what’s required.
Once configured, SendGuard will insert the keyword, and the email will be encrypted before delivery, ensuring secure outbound email encryption.
Admins can also enable this by default and lock the security settings screen to prevent users from disabling encryption.
Not all versions of Outlook support email encryption in the same way. The table below provides a quick overview of which platforms are compatible with Microsoft 365 Message Encryption or S/MIME.
| Outlook Version | Supports Encryption? |
| Outlook for Microsoft 365 | Yes |
| Outlook 2021 / 2019 / 2016 | Yes |
| New Outlook for Windows | Yes (some limits) |
| Outlook on the Web (OWA) | Yes |
| Outlook for iOS / Android | Yes (view only) |
| Outlook.com (Free Accounts) | Limited / No |
2. Automatically Encrypt Emails Using Rules
SendGuard can scan emails and attachments for confidential information and send encrypted messages if any sensitive content is detected.
This is done through the SendRules component of SendGuard.
Suppose we want to send secure email attachments in Outlook—for example, encrypting any outgoing message with a credit card number in the attachment.
You can do this by creating a rule. SendRules uses an intuitive IF/THEN approach. We will create the rule using the IF statement as shown below:
SendGuard includes pre-existing data loss prevention (DLP) templates that you can utilize, or you can create your own DLP policies tailored to your organization’s specific needs.
Next, we’ll add the appropriate condition in the THEN statement:
This will add the keyword “Encrypt” to the subject line, which in turn tells the email encryption software to encrypt the email.
SendGuard is an all-in-one SaaS-based solution for outbound emails, helping protect your business from accidental data leaks and compliance risks.
Here are other ways SendGuard protects your organization:
How to Further Enhance Outlook Email Security with SendGuard
While message encryption is vital, it isn’t the only line of defense. SendGuard offers comprehensive tools for business email encryption and risk mitigation.
Misdirected Email Protection
SendGuard scans recipient fields to prevent emails from being sent to the wrong person—helping you avoid autocomplete errors and maintain control over emails.
Scan Emails for Confidential Data
SendGuard includes built-in DLP rules to detect:
- Credit card numbers
- Social Security Numbers
- Patient Health Information (PHI) and Personally Identifiable Information (PII)
You can also create custom rules using keywords relevant to your business data.
Integration with Microsoft Information Protection Labels
SendGuard supports Microsoft sensitivity labels, detecting label values on email messages and attachments. Based on the label, it can block, warn, or require the user to verify before sending.
Reply-all Warnings
Warns users when replying to large groups or external domains, reducing the risk of accidental data exposure.
BCC Reply-All Alerts
If someone BCC’d on an email hits reply all, they could unintentionally expose their identity to other recipients. SendGuard prevents this by displaying a warning before each new message is sent.
Encourage Off-Email Communication
If email threads become too complex, SendGuard can prompt users to switch to Microsoft Teams or make phone calls, helping to avoid email fatigue and improve resolution speed.
Frequently Asked Questions about Adding Encryption to Outlook Emails
Does Outlook encryption encrypt attachments?
Yes, when you use Microsoft 365 Message Encryption (OME) or S/MIME with a supported version of Outlook, both the email and its attachments are encrypted.
This ensures that files sent with each new message remain protected from unauthorized access. The attachments are only accessible to recipients who have the correct decryption rights.
Note: If you’re using SendGuard to encrypt emails, ensure that your encryption software also supports attachment protection—most modern enterprise solutions do.
Can Outlook send encrypted email?
Outlook add-ins like SendGuard help automate encryption triggers based on user input or message content—ensuring encryption isn’t left to chance.
Note: S/MIME allows you to both encrypt and digitally sign a message. Digital signatures verify the sender’s identity and ensure the message hasn’t been altered. In some cases, such as requesting an encrypted receipt, you may need to enable both encryption and digital signatures.
How do you send secure email attachments in Outlook?
To send secure email attachments (Outlook), you must ensure your message is encrypted before sending. If you’re using Microsoft 365, click on Options > Encrypt while composing a new message.
This protects both the email message body and any attached files.
Note: With SendGuard, you can set rules to automatically encrypt emails based on the contents of attachments—for example, if a document contains credit card numbers or other sensitive data.
How do you manually encrypt an email before you send it?
To manually encrypt an email message in Outlook, follow these steps:
- Open a new message window.
- Click the “Options” tab on the ribbon.
- Select “Encrypt” or “Permissions“, depending on your version.
- Choose the desired protection level (e.g., Encrypt-Only, Do Not Forward).
In environments using SendGuard, users are prompted via the SendConfirm screen to choose whether or not to encrypt a message. This ensures that the decision is deliberate and reduces the chance of sensitive data being sent unprotected.
Where is the encryption option in Outlook?
The encryption option in Outlook is located under the “Options” tab when you’re composing a new message. Look for the “Encrypt” button. The interface may vary slightly depending on whether you’re using:
- Outlook for Microsoft 365
- New Outlook
- Outlook on the Web (OWA)
If you don’t see the “Encrypt” button, try looking under “Permissions” or clicking “More Options” in the ribbon. In the new Outlook, you may need to first enable S/MIME or Purview under Settings > Mail > Encryption.
Implement SendGuard in your Organization
Whether you’re using the new, original, or Outlook on the Web, SendGuard helps you meet security obligations, enforce best practices, and simplify email encryption.
Contact our sales team at sales@standss.com to learn more or request a free trial. If you’re an existing customer, we can assist you in configuring SendGuard to encrypt your emails and customize your deployment.
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