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 195.234.228.93 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?
Contact whoever told you to use those two DNS servers. Most likely, they are no longer configured to respond to your queries. This could be because you never had permission to use them and it was working by accident before. It could also be because someone inadvertently broke something.