A. Set Email to Yes (Use Default Settings).
B. Allow Sender Substitution for SMTP Mail Setup.
C. Set Email to Yes (Prompt for Settings).
D. Assign a Document Sending Profile to the Customer where Email is set to No.
E. Apply Office Server Settings to the SMTP Mail Setup.
F. Assign a Document Sending Profile to the Customer where Email is set to Yes.
Explanation:
Reference: https://docs.microsoft.com/en-gb/dynamics365/business-central/sales-how-setup-document-send-profiles