There are several causes for these two errors: the message may have been modified (perhaps by a mailing list or forwarder) in transit; the signature or hash values may have been calculated or applied incorrectly by the signer; the wrong public key value may have been published in DNS; or the message may have been spoofed by an entity not in possession of the private key needed to calculate a correct signature.
Any way you can check your DKIM entry for your MAIL-FROM domain here
I know this is an older post but, I ran into this issue yesterday. If you are using MailScanner for anti-spam efforts, try disabling the watermarking feature. I found the added watermark headers were invalidating DKIM hashes. Disabling the watermarks allowed the DKIM hashes to be valid. Yahoo was bouncing mail due to this.
As the above poster mentioned, I also had this problem. We use a windows server as our mailserver and we have antivirus installed on it.
It was setup to scan each outgoing message, but this changed the hash / body of each mail, thus failing the DKIM check.
So if you have this wrong body hash error, make sure you don't scan outgoing mails :)
