We are renting a Windows 2008 Hyper-V Webserver from a hosting company, from there we are sending mails using critsend, and all of a sudden, after working fine for a long time, smtp.critsend.com, the SMTP server we are using, cannot be resolved to an IP any more.
Other domains work well, and I couldn't find other examples for unresolvable domains.
The DNS servers used are 18.104.22.168 and .92.
I resolved smtp.critsend.com locally and added it to hosts, and the it worked - but it still worries me. Any ideas? Anything I can check to clarify the matter?