It could be a browser settings or browser security issue. Inferring your mail URL from your account, I'm able to access
mail.your-domain.com easily using the BETA of Edge...a site I've obviously never been to before in a BETA version of a new browser. Therefore, I'd check your browser security settings.
As an aside, I noticed there doesn't appear to be a SSL certificate attached to your mail domain. That may present an issue as well, down the line. I'd suggest you have your mail administrator add SSL to your mail URL.
Derek Curtis
COO
SmarterTools Inc.
(877) 357-6278
www.smartertools.com