Hi,
I have Google aps as a mail server, and also I use postfix for sending service emails via website like notifications about registration. I am going to set up DKIM on Google aps by adding txt record that Google provide. Do I need to add anything to this record to make my website email via postfix also pass DKIM autentification?

Unless you publish an ADSP record your unsigned mail will still "pass" DKIM checking, because the default is for the DKIM signature to be optional. So your signed mail from google will pass with a correct signature verification, and your unsigned mail from postfix will pass with no DKIM record.

However if you wish for your postfix mail to also be signed, you will have to set that up on your server. I personally use dkim-milter, but I believe there are several other packages you can set up to do your DKIM signing with postfix.

Thank you much, Stever