[exim] regex in an ACL

I am trying to detect Windows executable attachments in a MIME ACL. Assuming the
BASE64 encoding starts with TV[opqr], so I have

regex = \N\ATV[opqr]\N

I understood that the \A would anchor the test to the start of the attachment,
unlike ^ which anchors to the start of a line. Unfortunately, the test succeeds if
it finds TV[opqr] at the start of any line in the attachment.

Can anyone give me a test which will only search the start of the attachment?

Phil.
---------------------------------------
Phil Chambers (postmaster@???)
University of Exeter