Gmail's Delegate and collaborate on email allows adding delegates who are able to access someone else's mail box and read, delete and send from there. It states:

You can add up to 10 delegates. If you're using Gmail through your work, school, or other organization, you can add up to 1000 delegates within your organization.

Is there a way to use search operators to find only messages that were sent by a given delegate?

Examples that don't work:

sent_by:[email protected]
sender:[email protected]
X-Google-Sender-Delegation:[email protected]

Gmail's Delegate and collaborate on email allows adding delegates who are able to access someone else's mail box and read, delete and send from there. It states:

You can add up to 10 delegates. If you're using Gmail through your work, school, or other organization, you can add up to 1000 delegates within your organization.

Is there a way to use search operators to find only messages that were sent by a given delegate?

Examples that don't work (the latter two are what is actually shown in the full headers):

sent_by:[email protected]
sender:[email protected]
X-Google-Sender-Delegation:[email protected]