Can can support multiple authentication mechanisms for outbound SMTP including username/password and IP address. However these authentication mechanism do not work for customers who want to smarthost from G Suite or Office365. 


The limitation are:


  • username/password - G Suite and Office 365 do not support outbound smtp authentication to a smart host
  • IP address - G Suite and Office 365 do not have a static list of addresses that we can import for outbound smtp smarthost authentication


However there is another option, and this is to use your SPF record as an authentication tool for outbound smtp. 

As long as your SPF record includes outbound.mailhop.org and you are sending from an authenticated domain name on your account we can permit these services to smart host through the system. 


Use Case


We have a number of customers who route their emails via our service to authentication gateways like Zix. They however do not want to route ALL of their users through Zix, just the users in the accounting department. We then setup a routing rule that specifies a list of sender addresses and the smarthost that these emails get forwarded to, while the other messages are delivered directly to the Internet. 

We will DKIM sign all emails as it leaves the gateway to improve the authentication chain of the message. 


$listOfAddresses = [
    "user1@sendercom",
    "user2@sendercom",
    "user3@sendercom",
];

if ( $username == "customer" and in_array($sender, $listOfAddresses) ) {
    SetDestination("the.smart.host", 25);
}


We will DKIM sign all emails as it leaves the gateway to improve the authentication chain of the message.