To solve your send-to permissions issues for both Mac and Windows users, you can set send-to permissions on Exchange.
Users can still select the list in Outlook, but when they send, Exchange rejects it and bounces it back.
With PoliteMail, we bypass that check, so authorized PoliteMail users can send to those lists. This also prevents unauthorized users from sending to all-employees and other large distribution groups.
How to block send-to list permissions in Office365:
To achieve your 50% of users can and 50% can’t send to all, what other customers have done is the following:
1. Deploy our Syncronym tool to sync (certain) distribution groups with PoliteMail (e.g. the all-employees or any other protected list).
2. On the Exchange/AD side, hide these lists (set as hidden so users can not even access them from Outlook). For Exchange on-prem this can be done via PowerShell:
Set-UnifiedGroup -Id Group -HiddenFromAddressListsEnabled $True and synchronized via AAD with 0365
3. Set-up user groups within PoliteMail (e.g. All-Enabled), and add authorized users to the All-Enabled group.
4. Set list permissions for the synchronized protected list(s), to allow users from All-Enabled to View/Send.
In terms of add-in compatibility, we recommend testing. If you are still having difficulties, PoliteMail’s development team should be able to make them compatible if there is a conflict.
Setting these permissions will also prevent a dreaded Reply-All apocalypse.