To let a third-party mail using your own domain as sender and having properly implemented DKIM yourself you may come to realize that Plesk isn't helping you.
Some third-party mailers tell you to add a TXT-record containing their public key in your DNS.
This is not really the way to do it.
This way they will not be able to rekey their selector.
On top of never re-keying their selector these third-party mailers often have a 1024-bits key as they fit nicer into DNS. It becomes even more ugly...
Solution for adding DKIM cname records in DNS
Some third-party mailers tell you to add a TXT-record containing their public key in your DNS.
This is not really the way to do it.
This way they will not be able to rekey their selector.
On top of never re-keying their selector these third-party mailers often have a 1024-bits key as they fit nicer into DNS. It becomes even more ugly...
Solution for adding DKIM cname records in DNS