When you ask your ISP for a static-IP address, your service goes from Residential to a more expensive Business account, and they open up outgoing mail ports. (At least for Verizon FIOS that I'm on, pretty sure Comcast is same as well.)
Cloud IP addresses are probably more problematic for spam blocklists.
Glad it works for you. My comcast connection is far too unreliable to ever rely on for email!
Curious though, can you also set your own reverse DNS entry for your static ip? I’ve found many mail servers will reject your mail if rDNS records don’t match up.
I'm also running a server on a Comcast business service with a static IP. My service has been really stable. This must vary on area. Also it seems if you're on business class, the techs take you more seriously. When I did have some stability problems the tech they sent out did a few tests, then went to the entire first floor (5 units) of the condo building with big sticky notes telling them to schedule a service appointment or have their service blocked.
Getting reverse DNS was easy. Following the directions I found via Google I went into the Comcast business service forums, read their pinned posts and sent a PM to the current service guy. He set the reverse DNS for me. It took about a day.
I've never had to worry about reverse-DNS, and I email thousands of fashion/media/tech companies around the world, big and small. Are there really servers that block based on reverse-DNS? I've never seen it.
It seems to be a flaw to have reverse-DNS block mail servers, since a single mail server might serve multiple domains. (My server serves email for multiple domains)
