Would a sendable DE in SFMC created from Transactions (which would mean possible dup. emails) create duplicate Contacts in SFMC?

Question

I have been notified by SFMC that my company is over our Contact limit by >150% and I am having trouble pinpointing the issue.

Our All Sub list is under the limit, and the 2 DEs that we have set up via API for Contacts have the same contacts listed in them with identical Subscriber Keys from SF and from our primary retail site (so, these 2 DEs are not the issue).

Now, I have a theory of where these "other"/duplicate contacts are coming from, but I can find no literature on the subject and I am wondering if anyone here can answer.

A 3rd party had set up our retail site integration last year, and created sendable data extensions for Orders, Tracking Details, etc. Each of these lists has it's own primary Key of course and is sendable. My thought is that these sendable transaction-related DEs are creating duplicates or other/extra Contacts and are thereby causing this unexplained spike.

This is the best working theory I have so far, but I am unsure of it. If I am right, I will likely delete these transaction-related DEs as they are not needed.

Answer 1

Subscribers in all subscribers in email studio are just contacts that exist in the email application. Contacts however can be across different channels including MobileConnect and Mobile. In this instance, check that if you have any contacts from these channels.

Check the count of contacts that exist in contact builder All Contacts, look at the contacts source, some of them might have been incorrectly deleted or incorrectly created.

Raise a support ticket to check from where those contacts are and their backline team can delete duplicate subscribers.