More interesting data concerning my issue with @ubuntu.com email not working. It would appear that @ubuntu.com and list.ubuntu.com emails come from chlorine.canonical.com, but launchpad emails (which I previously tested as working) come from palladium.canonical.com.
When using several MX tools that show blacklists chlorine.canonical.com is listed as blocked and palladium. canonical.com is not.
The tools I used are:
- https://www.senderscore.org/blacklistlookup/ (return path)
Return Path originally listed the domain, but I was able to quickly ask that it be removed. I then tested several minutes later and it was no longer being listed. mxtoolbox.com still lists the site with two of its results; one of which was the one that blocks for four weeks unless you pay.
I am still waiting on a response from TWC on them white listing Canonical; I hope good sense prevails in that case, but we will see.