Reviewing and Understanding Default Connectors in Exchange 2016

After you install Exchange 2016, Microsoft loads default receive connectors on your email server. These connectors help you understand the way email enters into your organization.

Your Exchange server has two default roles – Mailbox and Edge Transport. The Mailbox server role is the important one to remember. It has three sub-roles called transport services.

The three services are:

1. Front End Transport Service: This service is the first step when email is received from another email server. It’s a stateless service for both incoming and outgoing emails.
2. Transport Service: This service supports queuing. It also categorizes emails. This is also the service where your antivirus and filters run.
3. Mailbox Transport Service: This service is similar to a routing service. It’s what retrieves emails from the database and delivers it to the transport service to send to other recipients. It also helps store email in the mailbox database.

You can view a list of receive connectors in the main Exchange Admin Center. Click “Receive Connectors” and then Mail Flow. This gives you a list of connectors in the center administration panel.

Here is a brief explanation of the five connectors you’ll see in this panel:

1. Client Frontend MBG : This connector is for secure connections. It’s for email sent with Transport Layer Security (TLS). It takes connections from IMAP and POP. It runs on port 587.
2. Default Frontend MBG : This connector takes connections on port 25, which you should recognize as the standard SMTP port. The received messages are then sent to the HubTransport connector.
3. Outbound Proxy Frontend: This connector is for outbound connections. It’s also for proxy connections. This connection is used if you have the “Proxy through client access server” checked in your sender settings in Exchange. It uses port 717.
4. Client Proxy : This is Exchange’s hub transport service. It’s the “middle man” between the frontend service and the mailbox transport service. It uses port 465 and accepts proxied IMAP and POP connections should they be set on the server.
5. Default : This is also the hub transport service. Just like the Client Proxy service, it also accepts email messages sent from the frontend service and sends any messages to mailbox transport services. The Client Proxy service accepts proxy services. The Default service just accepts messages and sends them to the mailbox service. IT uses port 2525.

Once you get used to the way these connectors work, you can better understand the way your Exchange server operates.