Virtual Identity is an extension / add-on for Mozilla Thunderbird and the Mozilla Seamonkey Suite. Using Virtual Identity you can simply edit the sender-address in your email to whatever you like – as long as your mail-server accepts the resulting mail. This is useful especially for people who have an own mail-server and don’t like adding every possible account as an Identity in the mail-client.
The feature to create instant, temporary Identities gives also increased possibilities to reply to other emails. Therefore the Virtual Identity extension contains a feature called Smart-Reply, which creates an identity based on information found in an received email without user interaction.
blog-entries about Virtual Identity are irregularily. If you are interested in up-to-date versions or like to file a bug-report, check the development page of Virtual Identity.