I've a website hosted in Dreamhost that uses Google Apps to manage mail. Now, i'm starting to fire some email marketing campaings using Campaing Monitor and I've failed in the Postini spam test.
Which DKIM is better to use, Google's one or CM's? Can't I use both?
Sorry if this question looks stupid, but i'm just starting to work with it.
I don't think you can use Google Apps to send email marketing campaigns. For one thing, I don't think DKIM signatures are added when you send through their SMTP servers - only when you send from the webmail interface. For another, I think there is a limit to the number of outgoing messages per day - at least for the free version of Google Apps. I could be wrong about those things, so you may want to check into them.
In any case, you can use DKIM with both Google Apps and Campaign Monitor - you just have to assign a different DKIM selector to each. A selector is basically a prefix that gets tacked onto the DKIM DNS TXT record. So, you can have one record with the prefix "ga" and another with the prefix "cm".
Please post back here if you find out any more detail - I am researching basically the same thing you are, and would like to learn more.