All tags or list columns can be renamed but 'Email address'. Furthermore, MaxBulk Mailer Pro offers 20 custom columns you can use to store recipient's data and insert it into your messages using Tags. Default tags are labeled Opt1 to Opt20. You can also rename those tags to something that will make more sense to you like [Address], [Suburb] and so on.
If you need to rename those optional tags for the whole application use the 'Preferences...' menu. But if you want to rename tags for only your current document, use 'Edit | Rename tags...' menu.
