If you are going to be running this from your main office or even several offices/places that have a Static IP or FQDN that uses Dynamic DNS, why not add a Receive Connector to your Office 365 Portal. Login to Office 365 Portal[^] with your Admin Credentials - Click Admin -> Admin centers -> Exchange -> mail flow -> connectors. Click + (New) -> From: Partner organization To: Office 365 -> Next -> Name: Bruce (what ever) -> Next -> Use the sender's IP address -> Next -> + (Add IP) 1.2.3.4 -> OK -> Next -> Select Security restrictions and click your way through. You should be able to side step TLS and still be somewhat secured through the connector.
Michael Martin Australia "I controlled my laughter and simple said "No,I am very busy,so I can't write any code for you". The moment they heard this all the smiling face turned into a sad looking face and one of them farted. So I had to leave the place as soon as possible." - Mr.Prakash One Fine Saturday. 24/04/2004