courier re-writing of mime boundaries, verification fails

[Mike Korizek]

Hi all

If courier receives an email with plain/text and HTML parts there
happens a re-writing of the MIME boundaries.
If the email is digitally signed with gnupg first, the verification
fails due to this re-writing.

I have no access to the server where courier runs on but I can
filter/process the email before it gets signed and sent to courier and I
can filter/process before it gets verified and sent to the mail client.

a) Is there a possibility to prevent the re-writing of the MIME boundaries?

b) If not, which are the rules of the re-writing. If I know them I can
reverse that before the verification happens.

--
Thanks for any hint.
Mike