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SMTP Relay in Exchange Server 2016

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In this article, we are going to discuss SMTP mail relay in Exchange 2016 versions of it. After that, the steps to configure receive-connector are mentioned. As the default setting, any of the MS Exchange Server versions could possibly receive emails on all of those domains, which are accepted and also configured in the organization. This precisely implies that theoretically, users could configure Firewall easily for publishing Public-IP-on-25-(TCP)-port to internal MS Exchange Server version 2016 and Internet’s email-flow would work appropriately. As the default setting, like all of the other earlier versions, any new Exchange Server’s deployment would be quite secure and there won’t be any risk of open-relays with that default setting.

Check In-Built Mail Relay Capability in MS Exchange Server Version 2016

  • Check those domains that are accepted with the help of either the MS Exchange-Management-Console or ECP i.e. Exchange-Admin-Center. As a default setting, any MS Exchange Server version 2016 would have multiple connectors that would be based on product’s transport-pipeline. Receive-Connector looks into is Default-Frontend. For getting there:
  1. First click on the mail-flow.
  2. After that, Receive Connectors.
  3. Also, ensure selecting of server from the list of Select-Server.
  • End-users can check & the result would be a fresh new message.
  • In this, the mail-flow has been tested & validated on receive-connector which is there by default. But, if we similar thing is tried to be done with the help of an external email address, an error would be received.
  • Seen from the perspective of safety and security, this surely is a good thing as, no unintended person would be able to use your MS Exchange Server version 2016 for relaying messages to any other domain that aren’t configured in this MS Exchange firm, but, for internal service or for internal application needing relaying of messages to some of the external users, this practice isn’t that good as one needs to allow this thing under those cases.

Configure Receive-Connector for Allowing Relay to External Address(s)

  • For allowing the external-relay, user needs the creation of a receive-connector.
  • Logged into the ECP or the Exchange-Admin-Center, Mail flow has to be clicked first.
  • Then Receive-Connectors.
  • Then, click New.
  • In new page, one has to label this new receive-connector.
  • After that, select Frontend-Transport.
  • Now, select Custom.
  • Then, click Next.
  • It is possible to bound the receive-connector to some particular adapter and/or to some port.
  • For this, it is needed to leave the default-settings, which are listening on all the server IPs and also on the traditional 25-port.
  • Then, click Next after that.
  • Till now, in the new receive-connector; values have been configured that are by now in place (Listening IP & port).
  • The only option for escaping any error while completing this particular wizard is by defining the Remote-network-settings-page with internal-servers’ IPs, which would relay the messages to the world outside.
  • The Exchange-Admin-Center can manage the security part.
  • Double-click on that new receive-connector.
  • And then, click Security.
  • Now, one can initiate easily by selecting some Anonymous-users where it is said that this relay would be open (which is not yet) with no authentication. This isn’t the very best of practices or the ideal ones, but could possibly be used under some of the controlled situations.
  • Next, you can configure some specific permission at the Receive-Connector-level.
  • If Get-ReceiveConnector is run, you would receive a complete list of all of the Receive-Connectors, but, isolating the connector is needed here.
  • Apply relay-permission to it.
  • For this, use \ after the cmdlet, Get-ReceiveConnector mtlex01\relay.
  • Having done this, apply Active-Directory-Permission by using the cmdlet, Get-ReceiveConnector \ | Add-ADPermission –User “NT Authority\Anonymous Logon” –ExtendedRights “ms-Exch-SMTP-Accept-Any-Recipient”.

External Mail Relay Test

After testing this internal relay, and creating a Receive-Connector for handling the External-Relay, one can initiate the testing process now. This can be performed by doing the same telnet-test by which one tried to send some mail message to some external mail. Also, at this point of time, the MS Exchange Server won’t refuse the connection but would allow going through it.

Ending Note

In the above blog, we managed to touch most of the aspects related to SMTP mail relay in Exchange 2016 and then we discussed how to configure internal as well as external receive-connector in MS Exchange Server version 2016.

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A Freelancer Tech Geek. Love to seek knowledge in technical arena and share it with folks. Did research on different technologies and like to share solutions to the problems.