BorderColors D is a Thunderbird extension that helps you avoid sending mails from the wrong account

Jan 30, 2021
Software, Thunderbird

Have you ever sent an email to the wrong recipient? Sure, it happens. Have you sent a mail from the wrong account? I have, and I think it's safe to say some of you might have done that too.

BorderColors D - default border dashed line

This is a common problem when you have multiple email addresses configured in your mail client. Some web services like Gmail have an undo option that can help save the day, or yourself some embarrassment, but it works only for a short period of time after you hit the send button.

Email clients don't have such an advantage. You hit send, and it does what it's supposed to do. It's not the program's fault.

BorderColors D is a simple add-on for Thunderbird that can save you from such issues as it highlights accounts by colors. Veteran Thunderbird users may be reminded of the Account Colors extension, which Martin reviewed in 2012.

Install the extension, and try sending a new email. You will see a border around the compose window; the color of the border represents the account that it is associated with. The default color is Light Gray and has a dashed line border. This border style is unique, if you change the color of the account that it's associated with, the style sort of disappears and there's no way to get it back. Well, you can, but you'll need to re-install the extension, which means you’ll lose your other settings.

BorderColors D is a Thunderbird extension that helps you avoid sending mails from the wrong account

If you change the sender account, you will see a different border color. Well, this is not configured by default, so you'll have to do it manually. Let's go to the add-on's options page.

BorderColors D lists each email account that you're signed in to in Thunderbird. Every one of these has a colored box next to it, click on the box and the standard color palette appears. Choose the shade that you want to set for an account, and make sure that you don't set the same one for multiple accounts.

BorderColors D addon settings

Next, you can choose your border style. Currently, the number of styles are limited (more on this at the end of the article), but there are still quite a few options that you can choose from.

The All Sides option displays a colored border on all four sides of the compose window. The next option, top and bottom border, removes the side borders. Toggling the top border displays a single line at the top of the window. There are four gradient options that you choose from which look kind of cool, so you may want to play around with it to find the one that suits you.

There is also an option to set a background color, but this one makes it difficult to read the text. BorderColors D lets you pick from three line-sizes, small, medium and large, which will change the thickness of the border accordingly.

Once you get used to it, the border serves as a quick reminder of the account that is selected. Make sure to set it up to your requirements. For example - Gray for your personal account, Red for work, Blue for your bank/finance related account, etc.

BorderColors D is an open source extension. It improves the features of legacy add-ons such as BorderColors and BorderColors-GT.

Colorblind users may want to use a different add-on called Identity Chooser, it displays a menu when you click on the "Write" button, that lists all your identities, and it makes you choose the sender every time you want to send a mail.

Note: Some of the options that the extension had before Thunderbird 78 was released aren't currently available. According to an issue filed on GitHub, these are due to limitations in the new Mail Extensions API. It's fine though, since even in its current state, we still get several styles to choose from and the add-on is perfectly usable.

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  1. owl said on February 16, 2021 at 10:19 am

    This is my favorite feature.
    I have many email addresses and multiple aliases, and I use properly them according to the destination and purpose. Thunderbird is the best way to centrally manage and operate them.
    Email is a very delicate private communication, and if it is sent to the wrong person, there is no way to cancel it or regain the message.

    To prevent this, I have added extensions “Identity Chooser”, “BorderColors D” and “Check and Send” to Thunderbird.
    By using this extension “BorderColors D”, I can visually check the e-mail addresses and aliases to be used, and thus prevent misuse. This extension is useful for users who utilize many e-mail addresses and multiple aliases.
    Extension Download Site (ATN)
    Official development support site:

  2. Niko said on January 30, 2021 at 2:43 pm

    I just uninstalled this extension after a year of use and then suddenly a review appears on “GHacks”! I can’t help but notice some parapsychological connection with the “GHacks” site! Hahahaha …

    By the way, this used to be part of the “Identity Choser” extension, which is also useful!

  3. JSands said on January 30, 2021 at 2:26 pm

    While open-source, the add-on requests “full, unrestricted access to thunderbird and your computer.”

    That’s more than a little off-putting and is going concern a lot of users.

    1. Ray said on January 30, 2021 at 7:27 pm

      JSands – That’s just Thunderbird’s default message for any addon requiring the use of older APIs via Experiments (

      A lot of addons require the use of the Experiment API because Thunderbird hasn’t ported over all the necessary older XUL ones over to the WebExtensions API yet. Unlike Firefox, Thunderbird allows experiment addons to be installed by default.

      I know this because I’ve written an experiment addon myself, although I’m only using the addon for my own use at this time.

      1. JSands said on January 31, 2021 at 3:51 pm

        I was aware that it was a default message and why. My point (which admittedly wasn’t clear) was that it might be off-putting to less-informed users and deserve a mention in the body of the article.

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