From my SMTP logs:
8/27 09:54:47p 4680 SMTP [147.185.133.84] !MISSING 'HELO' command (Received: 'User-Agent: Expanse, a Palo Alto Networks company, searches across the global IPv4 space multiple times per day to identify customers' presences on the Internet. If you would like to be excluded from our scans, please send IP addresses/domains to:
scaninfo@paloaltonetworks.com')
Hitting every SMTP port in IPv4 space looking for customers?
--- SBBSecho 3.20-Win32
* Origin: realitycheckbbs.org -- yesterday's tech today (46:1/115)