If you want to use Office 365 as your SMTP email server for a 3CX PBX you are best setting up a Connector on the Exchange Online account. I am assuming that your PBX is on the end of a static IP address.
First configure your 3CX server. Under Email and settings set the mail server to match your MX record. This usual follows the format domain.mail.protection.outlook.com where domain is your email domain with hyphens instead of dots.
Set a reply to address on the same domain. I always use pbx @ sfax.co.uk, it doesn’t go anywhere, I don’t expect anyone to reply to it.
You don’t need a username or password or to enable SSL/TLS as we will set up a connector to receive the email.
Next log on to your Office 365 portal as an administrator, and open your Exchange Admin Center. From there pick connectors under mail flow.
Create a new Connector.
Pick from: Your organization’s email server
To: Office 365
Give it an appropriate name:
Next select By Verifying that the IP address of the sending server matches one of these addresses that belong to your organization
Click the plus to add an IP address and enter your PBX’s internet IP address
Love using Gamma SIP trunks on 3CX, but it does annoy me that the built in SIP provisioning template doesn’t work well out to the box. I’m probably being finickity, but it would be nice if the templates just asked you what they need to work and put it where it should be.
So here is how we set up Gamma trunks.
First part is done for you out of the template. Use the Registrar server from the SBC section on the Gamma portal. They do have several, so don’t assume all your clients are the same.
Note format of Authentication ID. This is the main number that Gamma assign to the SIP trunk. We use E.164 format, not sure if changing that would change the format of this. Gamma authenticate using IP, but still need this to be correct.
Main trunk number is the main CLI that Gamma have given you routing is obviously your own.
We use CLI Flexibilty on most of our Gamma trunks which allows us to define the outgoing CLI that we present. Useful if, like us, you are using a non-geographic number, or are migrating to Gamma and want to use your existing numbers whilst they port.
We define our default caller ID here. This is the default, you can define individual ones under a users extension settings.
I’ve truncated most of the image because the template is correct, but to use CLI Flexibility you have to present a P-Asserted Identity to Gamma. This passes your authentication DDI as the From part of the SIP conversation will show the CLI you set above.
This is on 3CX v15, but the settings are the same for previous versions.