Hiding and unhiding Microsoft 365 Group

Members of all the Microsoft 365 groups will not be able to receive emails sent to those groups if they had not followed those groups in their Outlook as per the instructions in the article Follow an Outlook.com group in your inbox (microsoft.com)

To follow groups you have to unhide them using the command below,

Set-UnifiedGroup "groupname/emailaddress" -HiddenFromExchangeClientsEnabled:$false

Whereas if you wanted to hide them from the members completely, please refer to the cmdlet below

Set-UnifiedGroup "groupname/emailaddress" -HiddenFromExchangeClientsEnabled:$true

Note: 

• Please refer to the cmdlet below to get info about the group

Get-UnifiedGroup "groupname/emailaddress" | fl

• Please refer to Set-UnifiedGroup (ExchangePowerShell) | Microsoft Docs for more info
• Please refer to Not all members receive email sent to the group – CSP/MSP 24 x 7 Support (zendesk.com) for more info
  
  
• The HiddenFromExchangeClientsEnabled switch specifies whether the Microsoft 365 Group is hidden from Outlook clients connected to Microsoft 365.
   
  • To enable this setting, you don't need to specify a value with this switch. The Microsoft 365 Group is hidden from Outlook experiences. The group isn't visible in the Outlook left-hand navigation and isn't be visible in the global address list (GAL). The group name won't resolve during the creation a new message in Outlook. The group can still receive messages, but users can't search for or browse to the group in Outlook or Outlook on the web. Users also can't find the group by using the Discover option in Outlook on the web. Additionally, the HiddenFromAddressListsEnabled property will also be set to true to prevent the group from showing in the GAL and in the Offline Address Book (OAB).
  • To disable this setting, use this exact syntax: -HiddenFromExchangeClientsEnabled:$false. The Microsoft 365 Group is not hidden from Outlook experiences. The group will be visible in the GAL and other address lists. This is the default value.