Hi there, I have created a simple plugin for squirrelmail that allows you to login using an email address. The plugin will lookup the system username transparently from the virtusertable file. For me this works well on Debian Etch with Postfix and Squirrelmail (1.4.9) and a virtusertable file < 3000 lines. (It currently reads the entire file into an array.) Installs like any other plugin. Feel free to use. (This comes without warranty or support.)
