Can't Send Email from Client Email Programs

[Boris]

Windows 10 Home, SP1
ISP is Comcast at this vacation (not mine) home.
Windows Live Mail 2012
Thunderbird 78.11.0 (64-bit)
POP3
SMTP
both SSL
(been working for years)

The problem is that as of a few hours ago, I can no longer *send* emails
from either above client. I can receive just fine. If I use the Comcast
web mail, I can send and receive just fine.

I am not at my own home, but at a vacation home with a Comcast issued
modem/wifi router. All was fine this morning; I sent out emails ok.

Here are the messages I get when using email clients:

*When sent from Windows Live Mail 2012:
Your server has unexpectedly terminated the connection. Possible causes for
this include server problems, network problems, or a long period of
inactivity.

Subject 'Re: Family Files!'
Server: 'smtp.comcast.net'
Windows Live Mail Error ID: 0x800CCC0F
Protocol: SMTP
Port: 465 (or 587)
Secure(SSL): Yes

*When sent from Thunderbird 78.11.0 (64-bit):
An error occurred while sending mail: The mail server sent an incorrect
greeting: resomta-po-08v.sys.comcast.net resomta-po-08v.sys.comcast.net
Excessive failed authentication, ESMTP server temporarily not available.

If I immediately try to send again from Windows Live Mail 2012, I'll get
the same message I get from Thunderbird. One more try from Windows Live
Mail 2012, and I get the original WLM message.

What have I tried to fix:
reinstall WLM
reset the modem/wifi router by unlugging and replugging, letting lights
settle down
called comcast, they said 465 was wrong, to try 587, no luck
searched the Thunderbird message, and some implication that it means IP is
blacklisted

Later, I will go out and try to find a hotspot, and see if I get the same
messages. If not, I'd suspect the modem/wifi router in this house. But
that's just my non-techie guess.

By the way, my wife's Windows 10 Home laptop, running the same clients,
has the same problem, that arose at the same time.

[Boris]

Boris <Bo...@invalid.invalid> wrote in
news:XnsAD5A8E9F0DDF1B...@144.76.35.252:

I just got back from doing some road warrioring without the hacking. I
parked outside a Marriot Inn and logged into their unsecured wifi, and
was able to send emails. I then did the same thing outside a Walmart,
and all worked fine.

Hmmm...

When I came back here, all worked fine, both WLM and Thunderbird.

Was the Comcast server acting up intermittently? It wouldn't be the
first time.:

https://forums.xfinity.com/conversations/email/cannot-send-
email/602db07bc5375f08cd2f69f4

[Boris]

Boris <Bo...@invalid.invalid> wrote in
news:XnsAD5ACBE307CCBo...@144.76.35.252:

Crap. Here we go again. SMTP server is down. Just saying...