my emails are not delivered - ERROR_CODE :550, ERROR_CODE :DKIM

my emails are not delivered - ERROR_CODE :550, ERROR_CODE :DKIM

I am trying to email one of my clients and I get this message:

ERROR_CODE :550, ERROR_CODE :DKIM: encountered the following problem validating XXXXX.XX:
            bodyhash_mismatch

when I am emailing this same client from my gmail the emails are delivered.

Also when I am sending emails to my gmail also emails are delivered....

what is this error?

Cannot find information.....