Hi,
We have recently started to provide Email Archival services to our customers. We have a domain (abc.com) with individual Mailboxes for our clients (xyz@abc.com).
Since it's a public server, to reduce the amount of spam, I have configured my firewall to receive emails generated from list of specific IPs only. For example: We have a lot of customers who are using hosted email service from Rackspace. Rackspace was generous enough to send us the list of IPs of their machines that send us the emails. Similarly, I have configured receive rules for IP of customers who use their own Email servers.
This was a good until now, but we are getting customers who use Office365 and other services. I suppose its next to impossible to obtain list of Microsoft servers to add to my allow list.
Can anybody suggest a solution to this?