body hash signature did not verify

[Damian]

> All incoming mails are received by postfix, checked by
> amavis&spamassassin and
> delivered to the internal exchange server that forwards it to Office365
> Online Protection.
> 
> All mails with dkim signatures do have valid signatures when checked by
> amavis but
> if amavis relais them to exchange (and O365 checks DKIM again) we get a
> 
> dkim= fail (body hash did not verify)

Have you verified that the mail, as it goes out to the internal exchange
server, is already modified as seen in Office 365, e.g. via tcpdump?

> This happens anytime a german special char is in the email.
> Email without special chars have a working dkim body signature.
> 
> And it is definitely amavis – if I disable spamassassin or the anti
> virus agents the issues
> remain. If I disable amavis all mails got their dkim signature body hash
> intact …

How do you disable amavis? Do you bypass it completely?