tab characters in headers

Some users manage to get the Tab character (^I) in the headers, after the
Header and before the data.

For example

        Date:^IThu 4 Jun 1998
        From:^Ijoe schmoo <joe(_at_)mailexcite(_dot_)com>

This then throws off Formail when I go to extract the Sender email address,
with

        SENDER  = `formail -rtzx To:`

Has anybody solved this problem, or have any suggestions on how to work around.

Thanks

mark