Outlook Groups: who can send an email?

In an Outlook Group, being a member normally includes the ability to send messages to the group. The Trusted senders list is not usually an “only these people may send” list. It is used to allow selected people to bypass restrictions or moderation that apply to other senders, especially people who are not members.

Check the group’s Settings or Email/Send permissions page and look for the actual sending scope. If it is set to allow members to send, then every member can post to the group, as expected. To stop a particular person from sending, remove that person from the group or change the sending scope to owners only, if that option is available for the group type.

If the goal is a one-way announcement list where only the owner can send messages, an Outlook Group may not be the best fit. Use a group type or mailing list that supports owner-only posting, rather than relying on the Trusted senders setting.