I ran into this issue some time ago. You can read my case details below:
Case Question (sent to SF)
I am seeing sporadic behaviour in the following scenario:
- I have a Active subscriber on the All Subscribers list
- Their SubscriberKey is 1234 and email is firstname.lastname@example.org
- I do a real send from a data extensions to that same SubscriberKey (1234) but with a different email address (email@example.com)
In some cases, the email is sent to the new email address (firstname.lastname@example.org) and the email address for that SubscriberKey on All Subscribers has been over-written to be (email@example.com)
In other cases, the email is sent to firstname.lastname@example.org (regardless of the email specified in the send data extension), and the email address for that SubscriberKey on All Subscribers has not changed (ie: it is still email@example.com)
What is the actual behaviour supposed to be? Should the email address get over-written or not?
Answer I eventually got
Thank you for answering my call, as discussed over call, I have informed you that below are Only one of these processes would update the Email Address in Marketing Cloud:
- Manual change in the UI
- File Import to All Subscribers list (manual or via automation)
- Send to SF Report, SF Campaign or Salesforce Data Extension (Salesforce Send type)
Also In the all subscriber documentation the above points are not update, so I have provide the feedback to our knowledge team to update the article.
This case ran for a long time and was escalated all the way up, so I think there is some truth to it.
However, I don't think it covers all scenarios. For example, I am quite sure that sends initiated using the Journey API, for example, will also change the email address on All Subs in the instance where the "Send Tracking Results to Sales Cloud" check box is selected.
As you can see from the last sentence in their response, they promised they had passed on this info to the Knowledge team to update the documentation. I have followed up multiple times and the response from the knowledge team continues to be that this is not a "business critical issue, therefore it is remaining in the backlog as other items have higher priority". This was in April 2019.
So unfortunately, I don't think there is a clearly documented explanation of the scenarios in which the email address gets changed. Your solution to update them via an automation is the same as what we do.