Problem with SMTP EHLO host using Sugar On-Site

We are restoring a Sugar On Demand backup to an on premises server as we are migrating to On Site.

Everything is working fine, except email. I kept the configuration from the backup (which is fine), but got a new error (Sugar log files):

Wed Aug 24 15:07:42 2016 [2163][87471d16-9221-960f-dcb3-56ce37cd5749][FATAL] SMTP -> ERROR: EHLO not accepted from server. Code: 501 Reply: 5.5.4 HELO/EHLO argument "172.18.2.31/sugarcrm" invalid, closing connection. 501 5.5.4 https://support.google.com/mail/?p=helo u6sm4911857qtu.2 - gsmtp Wed Aug 24 15:07:42 2016 [2163][87471d16-9221-960f-dcb3-56ce37cd5749][FATAL] SMTP -> ERROR: HELO not accepted from server. Code: Reply: Wed Aug 24 15:07:42 2016 [2163][87471d16-9221-960f-dcb3-56ce37cd5749][FATAL] MailerException - @(SmtpMailer.php:166 [6]) - Failed to connect to outbound SMTP Mail Server

Well, looks like Sugar is sending the full qualified name of my instance (172.18.2.31/sugarcrm) to HELO and Gmail doesn't accept it.

I did a test using openssl: informing the instance qualifier (helo 172.18.2.31/sugarcrm) causes the same error. Sending only my internal IP (helo 172.18.2.31) works fine.

My question is: how can I change Sugar behavior so it sends only the IP, not the instance qualifier? Is there another way to solve it?

Thanks!