Assuming you want your mail to be handled directly by gmail (and remove blacknight entirely from the mail equation there - so no redirects required), you can set this up too. With google apps, you can use this for free for up to 10 mail accounts (it used to be higher, so the exact limit will depend on when you signed up for your app account), allowing you the benefits of the more familiar interface and spam filtering of a standard gmail account.
I assume this is actually what you wanted, but I'm not sure if it's what you've done or not (I'd guess so, but said I'd check). It depends on what tutorials you've followed. If it's not the way you're set up but would like it to be, let us know and someone will talk you through it.
Taking it a step further, for added security you should look at setting up an
SPF record for your domain. It makes it far more difficult for scammers to spoof your domain addy (commonly used for phishing scams) and also helps with the deliverability of your own mail (basically a positive mark to counteract any negatives in the heuristics scoring for mail spam).
What your basically doing is giving certain servers (in this case it will be the google mail servers, or the same could have been done using the Blacknight servers previously) permission to send mail on behalf of your domain. If I tried to send a mail from
scam@yourdomain.com from a different mail server, it would then be blocked as spam (rather than causing potential security risks for users believing they're speaking with someone connected to your business).
It's relatively simple to do, you just need to add a new TXT entry in your DNS settings along the lines of:
v=spf1 include:_spf.google.com ~all
(the "include" there is giving authorisation to the
google mail servers [if you're not set up with a google app account to handle your mail you'd need to provide the mail servers you're actually using] and the "~all" is creating a soft fail for anything coming from a different server [personally I'd go with a "-all", a hard fail, but it's six of one...])