Looks like Xepher.net has been added to a block list on hotmail.com and live.com.
Quotehost
hotmail-com.olc.protection.outlook.com[104.47.70.33] said: 550 5.7.1
Unfortunately, messages from [198.74.48.54] weren't sent. Please contact
your Internet service provider since part of their network is on our block
list (S3140). You can also refer your provider to
http://mail.live.com/mail/troubleshooting.aspx#errors.
[BN7NAM10FT044.eop-nam10.prod.protection.outlook.com] (in reply to MAIL
FROM command)
I will try to do something about it, but I've just about given up with Microsoft these days. Their website for SNDS (the place you go to resolve this stuff with them) is "currently experiencing technical issues" as well, so I can't even start the process of getting it sorted out. The server isn't blacklisted anywhere else on the internet, and yet MS somehow re-blocks it every couple of months, and it takes weeks to get them to remove it. The bottom line is that their system just sweeps up wide IP address ranges anytime there's a spam hit from any of them, and since this is a virtual server in a shared datacenter, I have zero control over who the "neighbors" are and what they do, yet I get caught up in the same net when one of them spams.
Finally got through to them again, and it's been "Conditionally mitigated." Which is their way of saying "unblocked" without admitting a mistake or even explaining why it was blocked in the first place.
If you use hotmail, PLEASE make sure to mark "not spam" any emails from xepher.net there, as apparently that's the only way for their system to start "trusting" the server here.
Note: it may take 24 hours for thing to start working they say. Please don't resend a bunch if it's not unblocked yet.