Email Validation Vendors

Our business is looking for an email validation partner that's Eloqua-friendly. I've searched the app marketplace and have found 4 vendors that might possibly work (FreshAddress, Experian, BriteVerify and possibly Synthio- though they appear do to more than email validation and could be a more expensive option....)

Also, it seems like the options for email validation occur either at the time of form submission or through providing the validation service a mass list which doesn't seem scalable. My ideal scenario would be to pull a contact into the campaign canvas as it becomes eligible based on the segment criteria, then after entering the campaign> go to email validation app> kick them out if invalid, else continue on in program. But that doesn't seem like any of the services really available.