Having trouble sending mail to mail.mil? You’re not alone. One of their three authoritative DNS servers (sdns3.csd.disa.mil) for the domain mail.mil appears to be unreachable right now. Confirm for yourself here.If you use public DNS, results are mixed. My testing shows that Cloudflare can find the MX record; Google Public DNS cannot.If you’re lucky enough where it’s easy to hard code an MX setting in your mail sending infrastructure, you could probably get away with temporarily directly mapping mail destined to mail.mil so that your MTAs just directly connect to IPs 184.108.40.206 – 220.127.116.11, as they seem to be responding just fine on port 25. (Those IPs are just a few of the mail servers that host mail for that domain.) Of course, that’s not a scalable long-term solution.I’ll update the website when more information is available.