Symantec Messaging Gateway fails to valildate a DKIM body hash signature that uses the "relaxed" algorithm for messages that have an empty body.
When Symantec Messaging Gateway sends an empty body message using the "relaxed" body hash signature, the resulting message will fail to validate on other DKIM enabled receiving Mail Transfer Agents.
Symantec is investigating this issue. This document will be updated when new information is available.
For outbound messages, use the "simple" algorithm for the body hash (this is the default configuration, so you may not need to make any changes):
Currently there are no workarounds available for inbound messages.