List Admins??? Ubuntu Users broken to Comcast and Yahoo emails

[P Echo]

There appears to be a problem with Ubuntu-users traffic going to
Comcast.net and Yahoo email accounts.

I am posting from my gmail account in hopes an administrator will see
and can correct.

History:
I have not received any emails from the list today at my Comcast.net
account.  Several test messages are from me.

I have been able to confirm that this problem is not just me or my
settings.  I spoke with a comcast security tech who attempted to
subscribe to the list from her comcast account, her yahoo account, and
her gmail account.  Comcast and Yahoo failed to even send the
confirmation email, Gmail worked.

The tech looked at the headers on the confirmation email as well as
the full headers I sent her from a message I received.  She says it
appears that everything is working on their end, no blocking or
anything else.  She also says they are willing to help, but would need
to discuss with someone who administers the list or the
lists.ubuntu.com servers to do more.

If a list admin wants to contact me off list, I would be happy to pass
along a phone number and "Ticket" number.  (Because my name / account
is associated with the ticket, I'd appreciate it if there is some
minimal independent verification of ID I can do . . . so I know you
are really an admin)

Thanks

--PE