You need to ensure, at the most basic level, that reverse name resolution works for your SMTP host (i.e. 137.117.203.77 must resolve to the Fully Qualified Domain Name (FQDN) you use in your SMTP headers). If this isn't true you'll most likely get mail rejected from most public SMTP hosts (gmail included).
Beyond this challenge (which you can control by setting up DNS correctly) you might still get rejected mail because a lot of blacklists will inlcude IP address ranges from Azure and AWS (this is why both offer mail services - SendGrid on Azure and Simple Email Service (SES) on AWS).