Microsoft has responded with an additional set of IP addresses in use for outbound traffic from Office 365.  We have programmatically added these new IP addresses to all customers for which we were able to detect current outbound activity from Office 365.  Customers that temporarily disabled the outbound relaying at Office 365 are encouraged to validate that these new IP addresses have been added to the authorized sending IP’s for their domain within the MAX Mail service.  With these additional authorized IPs, customers should be able to re-enable the outbound relay.

For reference, the IP addresses provided by Microsoft are as follows:

207.46.100.0/24
65.55.169.0/24
134.170.132.0/24
134.170.140.0/24
157.55.234.0/24
157.56.110.0/24
157.56.111.0/24
157.56.112.0/24