Check the Mail server configuration from the FaxMaker side: navigate to In-House Mail Server > Other SMTP or POP3 servers > SMTP server.
On the FaxMaker side, you only need to have an IIS SMTP server installed. Additionally, you will need to input the credentials of a Kerio account into the Email2Fax gateway settings of the FaxMaker.
On the Kerio Connect side, you will need to set up an SMTP relay rule, to direct the emails towards the FaxMaker server. Please create a new rule and input the server address of the FaxMaker server.
Emails to fax are being relayed through Kerio Connect.