BIMI promotes authentication, which is instrumental in protecting against some forms of abuse. BIMI’s goal is to promote message authentication and to allow brands to control the display of their logos in email they send. This solution aims to simplify the need for mailbox providers to support proprietary logo management systems.
BIMI allows mailbox providers to leverage a system that is meant to scale and allow providers to obtain logos from locations specified by the brands. Maintaining a proprietary system can be difficult, time consuming, and add additional support costs. BIMI provides a standard for mailbox providers to display the same logos across platforms. Additionally, it provides verification that logos are approved by a 3rd party.
No, a mailbox provider can make local determinations for individual domains. There is a draft BCP avaiable on the supporting documents page titled: Receivers Guidance for Implementing Branded Indicators for Message Identification (BIMI) for Mailbox Providers that discusses this in more detail.