Non-Member of Private Group able to email group - is this correct?

[Kathleen Lynch]

We have a private group, but recently received an email message from someone who is not a member of the group. I know that the private groups are listed in the

I thought private groups only allowed messages to be sent from other members.

Is this correct?

Thanks!

-kathy

[#2]

Internal users can send emails to a Group, even if it is private.

You can hide the Group email address from the GAL by PowerShell.

See https://techcommunity.microsoft.com/t5/Office-365-Groups/Hide-Group-email-from-global-address-list/m...

[#3 · Accepted solution]

If needed, you can impose delivery restrictions on the group (regardless if it's Private or Public) via PowerShell:

Set-UnifiedGroup groupname -AcceptMessagesOnlyFromSendersOrMembers groupname

You can designate a user, DG, another Group or whatever for the list of people allowed to send.

[#4]

So we hide an email address from the GAL. Once this is done, if I know the email address, but am not a group member, can I still send emails to it?  

I'm unsure if 'hidden' means 'not visible through' or 'not available to'. Thanks in advance.

[#5]

No, hiding from GAL doesn’t prevent mails sent to group! You can easily prevent external users to the organization to send mail to the group though from outlook and also through the powershell command Vasil posted above

Adam

[#6]

To clarify, the powershell can prevent mail from non-members overall

[#7]

Non members of the group or the organisation? 

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@adam deltinger wrote:
To clarify, the powershell can prevent mail from non-members overall

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[#8]

Sorry, the group :)

[#9]

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@adam deltinger wrote:
Sorry, the group :)

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That's great! Thanks :)

[#10]

@Vasil Michev @Kathleen Lynch  If you need to reverse the above command:

Set-UnifiedGroup groupname -AcceptMessagesOnlyFromSendersOrMembers $null

[#11]

This is good, I would just add you can also set a moderator or approver in addition to the setting below. Just in case it is something useful. You can set multiple moderators too.

Set-UnifiedGroup GroupNameHere -ModerationEnabled:$True -ModeratedBy UserMailbox

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@Vasil Michev wrote:

If needed, you can impose delivery restrictions on the group (regardless if it's Private or Public) via PowerShell:

Set-UnifiedGroup groupname -AcceptMessagesOnlyFromSendersOrMembers groupname

You can designate a user, DG, another Group or whatever for the list of people allowed to send.

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@Vasil Michev