Salesforce Contacts and Marketing Cloud Subscribers share a 1:1 relationship but behave differently than one another. Checkout the scenario below to better understand the intricacies between the two.

To start, it's important to understand:

1. Salesforce Contacts can have multiple email addresses on their record (Email, UCB, UCD, UCCS, SYS, etc). 
2. Marketing Cloud Subscribers can only have one email address on their record at any one time.
   • By way of sending to a Report or starting a Data Extension, a different email address can be associated to the same Subscriber.

For example, my Salesforce Contact has two different email fields populated:

• Email = meljones225@gmail.com [3]
• SYS Email = melanie.jones@cu.edu [4]

Let's say I just sent an Email through Marketing Cloud to a Report. The email address associated to my Subscriber reflects what's populated in the Email field (meljones225@gmail.com [3]) of my Salesforce Contact.

Now, I 'Start' a Data Extension pointing to the SYS Email field. Once processed successfully, the email address associated to my Subscriber is now what's populated in the SYS Email field (melanie.jones@cu.edu [4]) of my Salesforce Contact.

Subscriber Statuses & Troubleshooting [5]

If you come across any subscribers with any status [5] other than a green shirt (like red or gray), they are likely not receiving emails. Submit a help ticket [6] to remedy this (select Tell us what you need help with: Marketing Cloud >> Resubscribe Contact).