MoxiEngage pulls its contacts from your email Contacts/People list and can sometimes show duplicate contacts. Log in to your email and make sure that there are no duplicate contacts.
Cleaning Outlook Contacts
Outlook (both the software and the web app) will often link together duplicate contacts with the same name so you only see one. Technically, however, there are actually two. For example, one contact for the person just has an email and another just has just the mailing address. MoxiEngage sees both since technically there are multiple contacts.
To clean these up, log into the Outlook Web App (OWA) and go to the People section. Find one of the duplicates then click "Manage" on the Contact Card and see if there is a LINK/UNLINK option when you look at them. If this is present, you need to unlink them, then consolidate the information into one contact. Once you've done this, you can delete the duplicate.
Unfortunately, there is no easy or automatic way to do this - it has to be done one by one. However, when your contacts are cleaned up and consolidated, MoxiEngage shows the correct number of contacts!
Cleaning Gmail Contacts
To clean up your Gmail contacts please follow Google's Merge duplicate contacts guide.