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                3:24 p.m.
            
        I believe I figured it out.
I was updating user.display_name when the name I was seeing in Postorius was user.addresses[0].display_name.
Here are all of the steps for anyone looking to solve the same thing:
from mailman.interfaces.usermanager import IUserManager from zope.component import getUtility from mailman.testing.documentation import dump_list user_manager = getUtility(IUserManager)
u = user_manager.get_user('aperson@example.com') u.addresses[0].display_name = "Anne" commit()