dkim dns key are substandard

The ADSP dns key _domainkey.{domain} only existed in draft form. The resultant ADSP isn't that useful on a global settings as it will probably default to "unknown". This should be removed and let individual hosts add ADSP settings if it suits their policy. If anything _adsp._domainkey .. "dkim=unknown" as per RFC5617 would be a good default value.

For the DNS key itself I don't think hard coding t=y (testing mode) is a useful attribute. The impact of signing on emails has shown to have a positive impact on the delivery of legitimate email. I recommend removing not settin t=y. In rfc6376 t=s is recommended.

Also there are other parameters. http://www.iana.org/assignments/dkim-parameters/dkim-parameters.xml#dkim...

v=DKIM1 is recommended by http://tools.ietf.org/html/rfc6376#section-3.6.1

rfc6651#section-3.1 has r= to refer feedback about the signature. Recommend adding r=postmaster to the template.

Perhaps with all these options perhap a web interface that allows administrator editing in the following form:

v=DKIM1; k=rsa; r=postmaster; t=s; p=@PUBKEY

and virtualmin can populate @PUBKEY when it creates all the DNS records.