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SMTP On Premise Connector: Technical Requirements
SMTP On Premise Connector: Technical Requirements

Technical requirements : SMTP On Premise Connector

Kévin Joffray avatar
Written by Kévin Joffray
Updated this week

In order to configure the SMTP connector in your environment, please check the technical requirements:

Technical requirements

  • Applies to Microsoft Exchange On Premise Servers (2010, 2013, 2016 or 2019). If it is another type of mail server you must be able to apply the other requirements.

  • If there is an antispam in/out of the network, Letsignit must be between the client server and the antispam, otherwise the connector will not work.

  • A customer owned SMTP relay (anti-spam gateway, outbound filtering equipment or other) that can be reached on a public IP. This relay can be internal or external to the customer infrastructure.

  • Administrator access to the Exchange server is required to set up all the different connectors and routing rules.

SMTP configuration

To set up the Letsignit Cloud SMTP On Premise correctly you need to :

  • Create an outbound connector on your Exchange to forward them to :

  • Authorise and/or its Public IPs on your mail relay (internally set up or provided by a hosted solution and/or anti-spam) with a public IP. The mail flow will then take the following path:

    Exchange > Letsignit Cloud > Customer Relay / Anti-Spam > Final Recipient

  • SPF value to add to your DNS zone to allow Letsignit servers to be allowed to relay your mails (depending on the geographical area):

France / Europe:



  • In order to allow the automatic relay of emails with an empty sender (with a "From" value of ''<>''), we need an active and valid SMTP certificate ("Fingerprint") on your server, in order to add it to our servers' trust list.

Case on hybrid infrastructure O365

If you are in a hybrid infrastructure case, which means that you have one or more Exchange servers and a connection to an Exchange Online, it is necessary to know the last outgoing mail point.

If the mails are sent by the Exchange server, you must set up the SMTP On Premise connector.

If emails are sent via Office 365, please refer to setting up SMTP with Office 365.

In the case of emails coming from two or more sources, we recommend that the servers redirect their flows jointly to our servers, and then that we use the mail relay offered by Office 365, in which you will have to add, in addition to ours, the IPs of your Exchange server.

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