SMTP Diag Tool is described as 'is used to identify and troubleshoot SMTP server problems by trying to send a message to an SMTP server while displaying all diagnostic information in realtime in a log window' and is an app in the network & admin category. There are more than 10 alternatives to SMTP Diag Tool for a variety of platforms, including Online / Web-based, SaaS, Twitter, Mac and Windows. The best alternative is Pingdom. It's not free, so if you're looking for a free alternative, you could try intoDNS or MxToolBox. Other great apps like SMTP Diag Tool are Pingbreak, Curler by Amixr.IO, Up Ninja and Netthrob.
Pingdom web site monitoring and other infrastructure for you and instantly let you know when anything goes wrong. Measure uptime, downtime, and the performance of your website as experienced by visitors.
All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool. Input a domain name or IP Address or Host Name. Links in the results will guide you to other relevant tools and information.
Pingbreak is an original and free monitoring service. Get notified through Twitter if your website is down.
Pingbreak checks all of your websites each minute and alert you instantly by Direct Message (DM).
Monitor uptime,response timeandapdex indexes of your website or api for free and receive instant updates through e-mail or Slack with real time announcements. Don't leave your customers in the dark during downtime & outages of your website.
Unlimited monitors checked from multiple location every minute. Monitor any port or setup a "heartbeat" that works well for cron jobs or any service behind a firewall. Be alerted as soon as your service is offline via email or app integration.