REUSING DOMAINKEYS RECORDS
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Published DomainKeys key records are almost totally compatible with DKIM.
The one area in which they differ is the use of the granularity ("g=") tag.
Under DomainKeys, the default granularity is the empty string. DomainKeys
interprets this as "match anyone". However, DKIM interprets this as
"match none". Thus, a key record containing "g=" means one thing to
DomainKeys but the opposite to DKIM, making it incompatible.
Under DKIM, the default granularity is "*", which means "match anyone".
Since both systems have defaults that mean "match anyone", a DomainKeys
key record which doesn't have a "g=" string in it at all will work as
expected with DKIM. Thus, if you want to use one key record with both
systems, remove the "g=" portion of the record and reload your nameserver.