WebMail uses several tags to be filled in for particular information. For example, the max account size in KB is filled in for the MAXACCOUNTSIZEKB present in the default template. However, all templates can be customized by creating a copy of the template folder and editing the files. You also need to change the WebMail template path in the WebMail settings of AMS to point to the new template or add domain specific templates. You can then change the MAXACCOUNTSIZEKB to MAXACCOUNTSIZEMB to show the amount in MB instead and much more.
Please see
http://www.code-crafters.com/abilitymai ... lates.html for a full tutorial on editing the WebMail templates and all the available tags you can use.