How to Change a Message's Priority in Mozilla Thunderbird

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Mozilla Thunderbird lets you set the importance of an email you send, so the recipient might be alerted to key mail, for example.

Signaling Relative Importance

Not all email is equally time-sensitive. Use the Priority flag to reflect this urgency when you write and send a message in Mozilla Thunderbird, Netscape or Mozilla.

Depending on how important a message is to you (or how important you think it should be for the recipient), you can give it a low, normal or high priority.

Change a Message's Priority in Mozilla Thunderbird, Netscape, or Mozilla

To change the priority of an outgoing message in Netscape or Mozilla:

  1. Select Options | Priority from the message composition window menu. As an alternative, you can employ a toolbar button. Click Priority in the message’s toolbar.
  2. Select the priority that you want to assign to your message. 

Add a Priority Button to the Email Composition Toolbar in Mozilla Thunderbird

To add a priority button to the Mozilla Thunderbird message composition toolbar:

  1. Start with a new message in Mozilla Thunderbird.
  2. Click the message's composition toolbar with the right mouse button.
  3. Select Customize… from the context menu that has appeared.
  4. Drag, with the left mouse button, the Priority item to the spot in the toolbar where you want it located. You can position Priority in between attachments and security, for example.
  5. Click Done in the Customize Toolbar window.

The History and Importance of Email Importance Headers

Every email needs at least one recipient so every email has a To: field — and, perhaps, a Cc: field or a Bcc: field. Because you cannot send a message without specifying at least one addressee, these corresponding fields are well-developed in email standards.

A message's importance has, by comparison, never seemed so, well, important. This insignificance led to a proliferation of header fields for the purpose: everyone and their company rolled their own header or at least interpreted an existing header in new ways.

So, we have the "Importance:", "Priority:", "Urgency:", "X-MSMail-Priority:" and "X-Priority:" headers and there are possibly more.

What Happens Behind the Scenes When You Select a Message Priority in Mozilla Thunderbird

Mozilla Thunderbird employs and interprets exactly one of these possible headers when you send an email. When you change the priority of a message you are composing in Mozilla Thunderbird, the following header will be changed or added:

  • X-Priority
    • Takes the values from 5 to 1 in descending order, 5 for lowest and 1 for highest importance.
    • X-Priority is a non-standard email header; Importance would be a standard header.

Specifically, Mozilla Thunderbird will set the following values for the possible importance choices:

  1. Lowest: X-Priority: 5 (Lowest)
  2. Low: X-Priority: 4 (Low)
  3. Normal: X-Priority: Normal
  4. High: X-Priority: 2 (High)
  5. Highest: X-Priority: 1 (Highest)

With no priority set explicitly, Mozilla Thunderbird will also not include an X-Priority header.