Zgrab is apparently a kind of scan tool: https://linuxsecurity.expert/tools/zgrab/

In this case it tried to connect using the HTTP protocol, it might have tried with SMTP as well though.

I saw the following activity in my MercuryS window.  It's unlike any I've seen before.  The source IP belongs to DigitalOcean, LLC which is of concern because only two outside sales people use MercuryS.  Port is not standard, credentials are required, passwords are complex.  Insight into what I looking at would be appreciated.

T 20180323 103805 5ab49a46 Connection from 107.170.193.59
T 20180323 103805 5ab49a46 GET / HTTP/1.1
T 20180323 103805 5ab49a46 Host: XX.XX.XX.XXX:XXX
T 20180323 103805 5ab49a46 User-Agent: Mozilla/5.0 zgrab/0.x
T 20180323 103805 5ab49a46 Accept: */*
T 20180323 103805 5ab49a46 Accept-Encoding: gzip
T 20180323 103805 5ab49a46
T 20180323 103805 5ab49a46 Connection closed with 107.170.193.59, 0 sec. elapsed.