sending email to generic mail Id's from XS app

Hi Team ,

we are developing XS App on HCP , as per the requirement we need to send the email to the any generic email id's ( like sap.com or gmail.com or hotmail.com...,) from our xs appliation . so I made the settings in SMTP server as shown below and I build the xsjs service as well.

Now I can send the email to SAP Id's but not for generic mail id's .

when Im trying to send the email to gmail id's Im getting the reply mail as :

do I need to make any changes in the SMTP settings or how to address this

Please provide some idea or inputs

thanks in advance ,

Regards,

Madhu