Understanding message properties
Every incoming email is analyzed for specific characteristics called properties. These appear as small badges on the message detail page and can be used as conditions in filter rules. This article explains each property and how it is detected.
All 12 message properties
| Property | What it means | How it is detected |
|---|---|---|
| Multi-sender | The email was sent to multiple recipients | Multiple addresses in the To or CC headers |
| CC | You were CC'd on this email | Your alias appears in the CC header rather than the To header |
| BCC | You were BCC'd on this email | Your alias does not appear in either To or CC headers, but was in the SMTP envelope |
| Reply | This is a reply to a previous message | The email contains an In-Reply-To or References header |
| Forwarded | This message was forwarded | Subject starts with "Fwd:" or contains forwarding indicators in headers |
| Newsletter | This is a newsletter or mailing list | The email contains a List-Unsubscribe header |
| Attachments | The message contains attachments | MIME parts with Content-Disposition: attachment |
| Encrypted | The message is encrypted | PGP or S/MIME content type detected in the message body |
| Calendar | The message contains a calendar invite | Contains a text/calendar MIME part (iCalendar format) |
| Read confirmation | The sender requested a read receipt | The email contains a Disposition-Notification-To header |
| High priority | The sender marked this as high priority | X-Priority header set to 1 or 2, or Importance header set to "high" |
| Automated | The message was sent automatically | Auto-Submitted header is present and not "no", or precedence is "bulk" or "auto-reply" |
Using properties in filters
Properties are one of the 10 filter components. When you create a filter, select Property as the component, then choose which property to match.
Useful filter examples using properties:
- Auto-sort calendar invites — Property is "Calendar" → Allow, deliver to "Calendar" folder
- Flag high-priority emails — Property is "High priority" → Allow, mark as flagged
- Deny automated replies — Property is "Automated" → Deny
- Move newsletters to a folder — Property is "Newsletter" → Allow, deliver to "Newsletters" folder
How properties are stored
Properties are detected during inbound processing and stored as a compact bitmask on each message. This means they are available instantly on the message overview — no need to re-parse the email content.
A single message can have multiple properties simultaneously. For example, a newsletter with an attachment and a calendar invite would show three property badges.
