One of the worst things you can do to harm your campaign's contact rate, is to dial from unterminated ANI - meaning, placing outbound dials, from a phone number that can not be called back by the recipient...
The reasons for this happening, we've found, are many...
In the worst case, contact centers are robodialing, or random number generating, or some other type of unscrupulous activity, and simply don't care to receive the callbacks, which are assured to be complaints...thankfully, we don't come across that very much in our circles...and for those folks, we really do hope the SPAM gods throw down their wrath in full force... ;-)
Most commonly, though, what we find, is that the reason for this happening is plain old human error - someone makes a typo entering in the default ANI; someone copies a campaign and forgets to change the local presence config; maybe someone simply forgets to turn on the inbound campaign one morning, lol...
In any case, not only does such a mistake result in the inability to receive and convert inbound callbacks from potentially interested consumers, but to the SPAM detection algorithms, you look JUST LIKE one of the bad guys...
So make sure all of your i's are dotted and t's are crossed when it comes to which phone numbers are being used in your outbound dialing - one slip up will potentially harm ALL of the outbound phone numbers...its THAT fragile... :-)