How to Change a Message's Priority in Mozilla Thunderbird

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Setting priority (to high) in Mozilla Thunderbird usually gets you a visible "Beep". StockUnlimited

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


Not all email is equally important, and you can reflect that 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 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:
      1. Make sure you have added the Priority button to the message composition toolbar. (See below.)
      2. Click Priority in the message’s toolbar.
  2. Select the priority that you want to assign to your message.
    • ​​See below what effects the various choices will have

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 on 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 instance.
  1. ​Click Done in the Customize Toolbar window.

A Bit on the History and Importance of Email Importance Headers

Every email needs a recipient—or, perhaps, more than one; so, every email has a To: field—or, perhaps, a Cc: field, or a Bcc: field in addition. The importance of every email getting somewhere has led to a proliferation of header fields for the purpose.

A message's importance has, by comparison, never seemed so, well, important. This insignificance led, of course, 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.

(Updated August 2016, tested with Mozilla Thunderbird 45)