I am updating an email address in a Contact DE and then sending to a target DE that is updated with the new email address via a query. I want the email to be sent to that new email address and not the email address in the all subscribers. I am sending my email through a user initiated send in an automation. Is there a way to do this without exporting the email addresses and importing into the All Subscribers? Is the channel address order respected in Email Studio? Thank you.
All sends will automatically use the All Subscribers email address by default. To change this you will need to setup the DE as an Attribute Group in Contact Builder and create a 1:1 relationship back to the Contact record. The DE will need to contain an Email field.
You can then define the Channel Address Order by going to 'Contacts Configuration' > Edit > Add Address > Select new attribute group. Drag the new Channel Address to the top.
Here are some more discussions on this:
Contacts not getting added to all subscriber database
How to use a different email address in journey builder?
Contacts Configuration Documentation