Email, Messaging, & Video Calls Email How to View the Source of a Message in Mozilla Thunderbird by Heinz Tschabitscher Writer A former freelance contributor who has reviewed hundreds of email programs and services since 1997. our editorial process Heinz Tschabitscher Updated on September 19, 2020 Email Yahoo! Mail Gmail Tweet Share Email Mozilla Thunderbird is a cross-platform, feature-rich free email client with many customization and security options. If you'd like to check out the HTML source code of an email message, Mozilla makes it easy, whether from an unopened or open message. CC BY 2.0 / Flickr View a Thunderbird Email's Source Information If you'd like to identify a spam message's origins or troubleshoot problems with an email, viewing the message's source can be helpful. Highlight an unread message in your Thunderbird inbox. From the top menu, select View > Message Source. View your message's source information. Quickly view a message's source using a Thunderbird keyboard shortcut. Press Ctrl + U on a Windows or Linux PC, or press Command + U on a Mac. Alternatively, open an email in Thunderbird. From the top menu, select View > Message Source. View your message's source information. View a Message Source With Thunderbird's Menu Button It's also easy to access a message's source using Thunderbird's menu button. Highlight an email in your Thunderbird inbox. Select the Thunderbird Menu button from the top right. Select View. Select Message Source. View your message's source information. View a Message's Headers If you'd like more information about a message but don't need the source code, opt to view all of a message's headers. Select a message from your Thunderbird inbox. Select View > Headers. Select All. You'll see all the messages email headers.