Online Tools
VMware Licensing Calculator (unofficial)
DNSDumpster, dns recon & research, find & lookup dns records
ManageEngine Site24x7, Free Tools for Network, DevOps and Site Reliability Engineers (SRE)
Microsoft Portals, Microsoft Administrator Sites, Training, and Licensing Resources
dmarcian, Online tool to validate SPF, DKIM, DMARC
MXToolBox, a Multi-purpose validation tool
digicert, SSL Certificate Checker
SSL Labs, Vey a famous tool for deep analysis of the configuration of any SSL web server
Microsoft Remote Connectivity Analyzer, validate your Exchange, Skype for Business, or Office 365 configuration
Office 365 Anti-Spam IP Delist Portal
CheckTLS, CheckTLS tool to test email receiver
Vulmon, vulnerabilities Database
Subnet Calculator, Simple subnet calculator
