Microsoft 365 Groups in Outlook currently supports “Send As” functionality which enables group members to Send As a group (“From” address has group id) rather than as an individual. Group members should have this permission configured for the specific Groups by admins to make use of Send As capability. For the groups where user has Send As permissions enabled, user has the option to pick the groups account in the “From” address. Today, by default, the email loads up with individual email id in the From field when user compose, reply, reply all and forward messaged form group mailbox.
With this change, for users having the “Send As” permission for specific Microsoft 365 groups, when they compose, reply, reply all and forward mail from Groups mailbox then the default “From” address populated would be Group id instead of their individual id. This change will affect only when users are inside a group mailbox where they have Send As permissions. There will be no changes in behaviors in the personal/individual mailbox.