My machines hit on port which not published externally from public IP address

Hello,

My SMTP service running on VM receiving incoming connections from external IP address (which probably belongs to Azure). I did not publish this endpoint, so how come it makes it to my machine and what is purpouse of this traffic?

2015-07-03 21:21:12 168.63.129.16 - SMTPSVC1 CAPWEB2 10.0.0.8 0 QUIT - - 240 15016 3690 0 15016 SMTP - - - -
2015-07-03 21:21:27 168.63.129.16 - SMTPSVC1 CAPWEB2 10.0.0.8 0 QUIT - - 240 15015 3813 0 15015 SMTP - - - -