Admins Handbook

Office 365 sends emails from a lot of mailservers. retrys are often from a new IP.
Then you have delays of 5 min + 5 min etc…

Office 365 uses this IP’s:
https://technet.microsoft.com/en-us/library/dn163583

In your Mailscanner, you can Whitelist Office 365 Exchange IP’s by adding them to this:
/etc/sqlgrey/clients_ip_whitelist.local

OR
/etc/sqlgrey/clients_fqdn_whitelist.local
*.messageslabs.com
outbound.protection.outlook.com
*.outbound.protection.outlook.com
*.microsoftonline.com
*.hotmail.com

/etc/init.d/sqlgrey restart