Thunderbird's Most Underrated Feature: Identities

There are many good reasons to use Thunderbird 2 as your default desktop email client. Mozilla’s Thunderbird feature page lists some of them: advanced views, decent searching, security, junk mail screening, RSS feeds, add-on plugins and themes, cross-platform versions, and more.

However, there is one feature in Thunderbird that gets less press, yet is handled so beautifully as compared to other desktop clients it’s about time someone stood on a platform and sang its praises: identities. If you have ever had another email address ( forwarded to your “main” email ( and have been frustrated that your replies are appearing to be from instead of, you’ll want to understand how this underrated gem works.

First of all, you’ll need to be sure that the SMTP (outgoing) server you are using isn’t picky about what’s in the “From” field of your outgoing messages. Some ISPs (and hosts) will only allow you to send email through their server with a “From” domain that matches their email accounts. Identities probably won’t work in this case. I forward all of my email, both work and personal, through to an Island Email account (for spam cleansing) whose SMTP server does not have any problem with alternate “From” addresses. Authentication is by username & password.

In Outlook, and other desktop email clients you can easily set up multiple signatures and multiple accounts, using the “from” email address that you want to appear in your outgoing message. You just have to be careful that account is not checked to download new mail on a schedule (since you only care about outgoing messages for that account), and you have to remember to select the correct account/signature on each message that you want to appear to be coming from that address. So if you hit reply on an email addressed to but it was received from the account, it will use as the “From” address along with the signature set for that account unless you manually change the account to before sending the message.

With Thunderbird, you do not have to remember to manually select the account you want. Thunderbird will look at the email the message is sent to, and will automatically select the proper identity when you reply. If you manually switch identities on your outgoing message, the signature file, formatting preferences and what will happen to the message after you send it switches on-the-fly.

Mozilla, you had me at hello.

Start with the default identity, and click the “Manage Identities” button on the screen:

You’ll see the default identity you established above. Click “Add…” to create a new one.

Enter in the information you want recipients to see. The key to identities is that you’re not entering the server address or username. It’s only about outgoing messages, and it links the outgoing action based on a matching email address in a received message’s “To:” field. How smart is that? This is much easier and more powerful than setting up a complicated system of accounts, filters and rules that act on that field.

Here you can tell Thunderbird what to do with email that is sent from that identity. Maybe you have a separate folder just for sent mail from that alternate address? Outlook or would require you to set up a separate rule/filter to make sure those messages are filed separately. Thunderbird makes that easier.

Finally, you can change the formatting of your post and quoting style based on the outgoing identity.

Think about compiling all your various email accounts into one bucket, and then using this feature in Thunderbird to effortlessly switch back and forth between all the different email accounts you have, with only one mailbox to check and manage. Hit “reply” to an email addressed to a work-related address without worrying about your casual, personal contact information accidentally left at the bottom as you juggle signature file settings.

Personally, this is the killer Thunderbird feature that is the reason I haven’t launched Outlook in nearly a week. It’s not even new to Thunderbird 2. It was introduced in Thunderbird 0.5 (without the GUI to easily manage it). I just didn’t realize it existed before.

What’s your favorite underrated Thunderbird feature? Share in the comments.


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