Do not disturb
I work on call all the time based on emails from a specific email sender. How can I restrict alerts and notifications only to a specific sender via email when using do not disturb or focus settings?
Though I am not clear with your requirement because you first said, "I work on call all the time based on emails from a specific email sender." then you added "How can I restrict alerts and notifications only to a specific sender via email"
However, the pic given below depicts scenarios based on my understanding and is self-explanatory.
Note (Focus): Mail notifications will work seamlessly for mails which has a Push notification feature and may not always work for Fetch type of mail settings
Google, AOL, Yahoo - Only the Fetch mail Option is available
iCloud, Exchange, Outlook - Both Fetch and Push Mail option is available