We have our inhouse tool to check the SMTP settings shared by the customer, its highly recommended to use the tool for the troubleshooting purpose and for the pre installation form received consisting of the SMTP details, keep sharing the feedback to the account manager for the same.
Inhouse SMTP test tool : http://101.53.157.241:6019/
SMTP TEST TOOL URL: https://www.gmass.co/smtp-test
1) Login to your gmail account.
2) Go to https://www.google.com/settings/security/lesssecureapps and Turn On this feature.
3) Go to https://accounts.google.com/DisplayUnlockCaptcha and click Continue.