A client we manage their Office 365 tenant for are looking to reduce email outside of workings hours from internal employees to help reduce workload and stress.

We would like to either stop it from sending entirely sender side (i.e. an email sent at 7pm is delayed to be sent to the receipient until 9am the next day).

Or for the server to queue on behelf of the user, so it doesnt deliver outside of working hours.

Ideally we would want exceptions to the above, incase from a specific manager (as an emergency) or from external emails.

I have seen an addin from https://www.ivasoft.com/ but these are client side and seem to be for Windows - this is a mix of Windows and Mac users on Outlook, and would be a very manual process to install agents so ideally server side policies.

We would be ok to have them use the web browser outlook.office.com exclusively and retire the desktop based Outlook.

If not with Office 365, what other mailservers (i.e. google etc) would offer the above mailflow features.

Update for Microsoft Viva

As an update, I'm picking up reporting to drive cultural change and policy is the way to go here... Microsoft Viva looks like it will give all the data on offenders for coaching by employee welfare officers (coupled with reports after hours, number of people being CC etc). Microsoft Viva also has a plugin to delay sending will need to check of this works with mac.