OnPrem SMTP sending to Office 365 Encrypted

[David Kamp]

I have Internal servers relaying on a "on premise SMTP server" this smtp server has an Office 365 Exchange Connector configured a:

From: Your organization's email server

To: Office 365

Identity: from our Public IP that the smtp server sends from.

All works Great.

Now I have been asked if we can have the message encrypted or use TLS between the smtp server and Office 365.

Can that be done? without encrypting from every account that is being relayed.

if so how?

Thank you

David

[#2]

Set the connector to require TLS as detailed for example here: https://technet.microsoft.com/en-us/library/dn751021(v=exchg.150).aspx

[#3]

Hi David,
By default when you run Hybrid Configuration Wizard it will configure the TLS base on you certificate by default.

[#4]

When I edit my Connector, On the question of: How should Office 365 identify from your Mail server? I am selecting my IP Address and then do not have an Option for TLS and the summary does not indicate TLS.

[#5 · Accepted solution]

It's generally assumed that when you configure TLS, you would use a certificate associated with specific domain, so that the service can verify the sender. If you use the IP option, you should still be able to toggle the TLS requirement via PowerShell:

Get-InboundConnector Hybrid-In | Set-InboundConnector -RequireTls $true

[#6]

I ran the command to force TLS, Now Powershell shows "RequireTls: True

This is the result log file on my smtp server does it look to be secure?

*****

2018-04-24 12:01:14 216.32.181.10 OutboundConnectionResponse - 220+CO1NAM03FT006.mail.protection.outlook.com+Microsoft+ESMTP+MAIL+Service+ready+at+Tue,+24+Apr+2018+12:01:14++0000 94 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionCommand EHLO smtp.XYZ.org 94 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionResponse - 250-CO1NAM03FT006.mail.protection.outlook.com+Hello+[XX.XXX.XXX.XXX] 157 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionCommand STARTTLS - 157 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionResponse - 220+2.0.0+SMTP+server+ready 219 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionCommand EHLO smtp.XYZ.org 360 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionResponse - 250-CO1NAM03FT006.mail.protection.outlook.com+Hello+[XX.XXX.XXX.XXX] 407 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionCommand MAIL FROM:<imagenow@XYZ.org>+SIZE=1110 407 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionResponse - 250+2.1.0+Sender+OK 516 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionCommand RCPT TO:<JoeBob@XYZ.com> 516 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionResponse - 250+2.1.5+Recipient+OK 610 SMTP -
2018-04-24 12:01:14 216.32.181.10 OutboundConnectionCommand BDAT 1110+LAST 610 SMTP -