I have a Comcast Xfiniti Business line, 5 static IP addresses, etc. It sounds like our mutual set ups are equivalent. I've been running my email servers in my own domains since 1998, through some gone ISP, PacBell/AT&T, and Comcast without issues.
Contact the Comcast business line. Have your actual account ready -- you can get that from the Comcast Business web page for your account. Those numbers changed in the last 12 months to a shorter, simpler format. Request technical support and discuss the issue.
One thing that you MUST do if you want to run your own email: request that Comcast set reverse DNS to point at your servers for the non-authoritative request. A reverse DNS request to your IP address must return the name you use for your primary (and secondary, and so on) MX records. If that's set up, then you've solved 90% of the issues with Gmail and Yahoo!.
As far as Hotmail: they've been rejecting my email unless users white list my address(es) in their individual accounts. This has happened since Microsoft bought them. No way around that, and no appeals; every time I tried to contact them I might as well have sent the emails/requests through a black hole.
Source: 8+ years with Comcast Business, and I moved to a new location (with new IP addresses and new routers) 12 days ago. It took them 10 minutes to set the rDNS and propagate. Within an hour it was resolving fine and any lagging email issues were resolved (36 hours of some undelivered messages).
Google my name "Eugene Ciurana" and ping me through my contact page if you want some assistance with your set up and/or other tips w/dealing with Comcast. I've been a very happy customer with them (they fixed my lines, including physical cable modem replacement due to physical failure, while I was out of the country last January and coordinating with someone who could open the door to them and so on), and in general found that, if you explain what you need and why, their tech guys do work with you to solve issues. The key is understanding that *you* may know more about networking/server set up than their tech guys, so if you aren't specific about what you want they may not grok what you need.
Dear admins: WTF is a lameness filter? What is it filtering? I couldn't offer complete information to this guy because of the Comcast support number and/or IP addresses I listed. With my Karma level and the number of years I've been around, your system ought to be configured to let stuff through w/o issue. Look at my user ID. Thanks.