Help needed with possible DNS related issue with Comcast mail servers

[tomdkat]

Hi! Starting on Monday, November 19, 2018, Thunderbird on two Ubuntu systems I use can't connect to Comcast's POP3 mail servers. One system is running Ubuntu 18.04 and the other Ubuntu 18.10. Both are 64-bit systems and both are running Thunderbird 60.2.1. Thunderbird issues a "Failed to connect to server mail.comcast.net" message and I can't retrieve new mail. So, I did some research and experimentation and found the following:

• Thunderbird can connect to Comcast's IMAP servers just fine
• I can't ping mail.comcast.net
• I can do DNS lookups on mail.comcast.net just fine

When I ping Comcast's mail server address, I get this:

tom@deathstar:~$ ping mail.comcast.net
ping: mail.comcast.net: Name or service not known
tom@deathstar:~$

When I do DNS lookups on "mail.comcast.net", I get addresses back:

tom@deathstar:~$ nslookup mail.comcast.net
Server:		127.0.0.53
Address:	127.0.0.53#53

Non-authoritative answer:
mail.comcast.net	canonical name = imap.ge.xfinity.com.
Name:	imap.ge.xfinity.com
Address: 96.118.242.209
Name:	imap.ge.xfinity.com
Address: 96.118.242.197
Name:	imap.ge.xfinity.com
Address: 96.118.242.233
Name:	imap.ge.xfinity.com
Address: 96.118.242.225
Name:	imap.ge.xfinity.com
Address: 96.118.242.226
Name:	imap.ge.xfinity.com
Address: 96.118.242.217
Name:	imap.ge.xfinity.com
Address: 96.118.242.208
Name:	imap.ge.xfinity.com
Address: 96.118.242.230
Name:	imap.ge.xfinity.com
Address: 96.118.242.232
Name:	imap.ge.xfinity.com
Address: 96.118.242.218
Name:	imap.ge.xfinity.com
Address: 96.118.242.211
Name:	imap.ge.xfinity.com
Address: 96.118.242.242
Name:	imap.ge.xfinity.com
Address: 96.118.242.221
Name:	imap.ge.xfinity.com
Address: 96.118.242.196
Name:	imap.ge.xfinity.com
Address: 96.118.208.40
Name:	imap.ge.xfinity.com
Address: 96.118.208.99
Name:	imap.ge.xfinity.com
Address: 2001:558:fc11:9:f816:3eff:fee8:4f07
Name:	imap.ge.xfinity.com
Address: 2001:558:fc11:9:f816:3eff:fe7d:1b0c
Name:	imap.ge.xfinity.com
Address: 2001:558:fc11:9:f816:3eff:fe25:5ae5
Name:	imap.ge.xfinity.com
Address: 2001:558:fc11:9:f816:3eff:fef6:babc
Name:	imap.ge.xfinity.com
Address: 2001:558:fc11:9:f816:3eff:fe87:c172
Name:	imap.ge.xfinity.com
Address: 2001:558:fc11:9:f816:3eff:fee6:7a57
Name:	imap.ge.xfinity.com
Address: 2001:558:fc11:9:f816:3eff:fe0f:a4a
Name:	imap.ge.xfinity.com
Address: 2001:558:fc11:2:f816:3eff:fec7:cb93
Name:	imap.ge.xfinity.com
Address: 2001:558:fee2:1000:f816:3eff:fe42:4f14
Name:	imap.ge.xfinity.com
Address: 2001:558:fc18:0:f816:3eff:fe33:9aaa
Name:	imap.ge.xfinity.com
Address: 2001:558:fc18:0:f816:3eff:feb2:8c0d
Name:	imap.ge.xfinity.com
Address: 2001:558:fc18:0:f816:3eff:fef1:25a5
Name:	imap.ge.xfinity.com
Address: 2001:558:fc18:0:f816:3eff:febd:320a
Name:	imap.ge.xfinity.com
Address: 2001:558:fc18:0:f816:3eff:fe36:aba3
Name:	imap.ge.xfinity.com
Address: 2001:558:fc18:0:f816:3eff:fe3f:76f2
Name:	imap.ge.xfinity.com
Address: 2001:558:fc18:0:f816:3eff:fe45:1d1e

tom@deathstar:~$ dig mail.comcast.net

; <<>> DiG 9.11.4-3ubuntu5-Ubuntu <<>> mail.comcast.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15037
;; flags: qr rd ra; QUERY: 1, ANSWER: 17, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;mail.comcast.net.		IN	A

;; ANSWER SECTION:
mail.comcast.net.	15	IN	CNAME	imap.ge.xfinity.com.
imap.ge.xfinity.com.	12	IN	A	96.117.3.119
imap.ge.xfinity.com.	12	IN	A	96.117.3.96
imap.ge.xfinity.com.	12	IN	A	96.117.3.143
imap.ge.xfinity.com.	12	IN	A	96.117.3.145
imap.ge.xfinity.com.	12	IN	A	96.117.3.129
imap.ge.xfinity.com.	12	IN	A	96.117.3.148
imap.ge.xfinity.com.	12	IN	A	96.117.3.201
imap.ge.xfinity.com.	12	IN	A	96.117.3.136
imap.ge.xfinity.com.	12	IN	A	96.118.133.238
imap.ge.xfinity.com.	12	IN	A	96.117.3.128
imap.ge.xfinity.com.	12	IN	A	96.117.3.144
imap.ge.xfinity.com.	12	IN	A	96.117.2.238
imap.ge.xfinity.com.	12	IN	A	96.117.3.110
imap.ge.xfinity.com.	12	IN	A	96.117.3.140
imap.ge.xfinity.com.	12	IN	A	96.117.3.154
imap.ge.xfinity.com.	12	IN	A	96.117.3.132

;; Query time: 13 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Tue Nov 20 06:58:31 PST 2018
;; MSG SIZE  rcvd: 334

tom@deathstar:~$

I have no problems accessing mail through Comcast's website and other sites work fine. I can access email on non-Comcast servers just fine. On Sunday, November 18, 2018, Thunderbird *was* able to access Comcast mail via POP3 just fine. Clearly, something changed and I think it was probably something on the Comcast side, with the POP3 mail server address being changed to a CNAME of the IMAP mail server address.

The reason I'm posting this is to find out how I can fix the "ping" issue and the "Failed to connect to server" issue Thunderbird is experiencing. On a Linux Mint 18.3 system I also use, I'm able to ping "mail.comcast.net" just fine and Thunderbird (60.2.1) has no problems accessing my mail using Comcast's POP3 mail server. So, I'm looking for help in troubleshooting and resolving what might be DNS lookup related issue that's preventing Thunderbird from accessing Comcast's POP3 mail server.

I'm using the "Ubuntu 18.04/18.10 stock" DNS related configuration settings, meaning I haven't changed anything. My Ubuntu 18.10 system has an Ethernet connection to my TRENDNet router and I use a Netgear cable modem. Outside of the Thunderbird issue, my Internet access works well.

My /etc/resolv.conf file contains the following:

tom@deathstar:~$ dir -l /etc/resolv.conf
lrwxrwxrwx 1 root root 39 Jan 15  2018 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf
tom@deathstar:~$ cat /etc/resolv.conf
# This file is managed by man:systemd-resolved(8). Do not edit.
#
# This is a dynamic resolv.conf file for connecting local clients to the
# internal DNS stub resolver of systemd-resolved. This file lists all
# configured search domains.
#
# Run "resolvectl status" to see details about the uplink DNS servers
# currently in use.
#
# Third party programs must not access this file directly, but only through the
# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,
# replace this symlink by a static file or a different symlink.
#
# See man:systemd-resolved.service(8) for details about the supported modes of
# operation for /etc/resolv.conf.

nameserver 127.0.0.53
tom@deathstar:~$

As part of my online research, I did find this article:

https://moss.sh/name-resolution-issue-systemd-resolved/

which basically states systemd-resolved doesn't support RRSIG and I was able to get some of the test results posted in that article on the Ubuntu 18.04 system I use.

In any event, this is where I'm at now. What's the best way to diagnose the cause of both ping and Thunderbird's inability to contact Comcast's POP3 mail server "mail.comcast.net"?

Thanks in advance!

[walts48]

It appears that tomdkat and I are the only Comcast users on Linux.

I have the same problem, get the same ping results and today my Verizon POP3 account connection fails in Thunderbird.

I'm wondering if any of the Bind9, systemd, libnss or any of the recent updates broke something?

[lisati]

@walts48:

Please be patient. The forum community is made up of people from all around the world who live in different time zones, who don't always get to see support requests when first posted.

[cscheppner]

I also use Ubuntu 18.04 and Comcast email w/ Thunderbird and I am experiencing the same issue (though I had been using pop.comcast.net port 995). My Thunderbird w/ Comcast email worked fine for 4+ years on 3 LTS versions of Ubuntu/ It was working fine on Friday Nov 16. 1018. I came into work yesterday Nov 19, 2018 and Thunderbird was unable to connect to the incoming Comcast mail server (though it could connect to outgoing smtp).

I did find a hacky workaround...

In a shell I did nslookup mail.comcast.net
I copied the IP of the first non-authoritative answer (there were only non-authoritative answers).
I pasted that IP into the Thunderbird Preference..Account Settings..Server Settings .. Server Name
(my other settings are SSL/TLS and port 995 because I use pop)
Then clicked OK.

Then when I tried to Get Messages, I got a popup error about a certificate not matching and did I want to override...
I did do a temporary override, then was prompted for and entered my email password, and Thunderbird retrieved my email.

Probably not the most secure safe way to get my mail, but I got my mail.

[localjoe]

I have had the exact same problem in the last two or three days or so and cscheppner's solution worked for me. I has to substitute an IP address for the string "pop3.comcast.net" in Thunderbird's Server Settings / Server Name.

I am running Thunderbird 60.2.1 64-bit on Linux Ubuntu 18.04.1 LTS

While searching before finding this thread I saw a thread on another forum (I wish I could remember where ) that postulated that someone's (Thunderbird's) certificates from Symantec were now obsolete. But I don't know enough about it so cannot verify that theory.

Well at least I have my email now.

Thank you cscheppner

[1clue]

I had comcast years ago, and used it with Linux. Stopped about 6 or 7 years ago when I moved to a different state.

I had issues with DNS from Comcast servers too, and so did other people I knew.

I came to suspect that they messed with DNS resolution based on what type of customer you were. I had frequent long delays in name resolution of highly trafficked sites, like google.com or yahoo or news sites. Seconds-long.

In my opinion at that time, I suspected that if you had a minimal Internet account they would slow you down so you would upgrade. The speed tests would do a DNS search at the first and then handle a single connection for the entire test, so it was rated speed. A news site or typical commercial website has a bunch of connections from a bunch of different servers with almost every page load. You could mess with TTL and cause the browser to hit the DNS server more often, and delay the response from the DNS to slow down the user experience.

I also suspected them of "losing" popular sites when your payment was late, and that when they shut off your service they actually just told your DHCP server to assign a different DNS that doesn't exist.

I set up a few scripts to test some of those theories, and one part of it was that I would use google's DNS server, and had a script to copy my version of /etc/resolv.conf over the top of whatever was there. I could bring up a disabled account that way.

[rempat]

I discovered the same problem on November 20, 2018. Comcast customer service were no help. The workaround from cscheppner is getting my emails and I am thankful!

[QIII]

You will need to set up an imap account -- in Thunderbird, not with Comcast -- using your current Comcast account. Then you will have to rename the current account to avoid getting an error and build folders in the new account that match your current account. Following that, you will have to go through a tedious process of copying emails from each folder in the old account to the corresponding folders in the new account. Then delete the POP account from Thunderbird.

This might help.

And, yes, please be patient. Don't expect everyone to jump on every new post. We all have lives outside of the Forum. None of us works for Canonical and we all volunteer our time as we have it to give. I only just saw this post. I have Comcast, use Thunderbird, ran into the same issue and fixed it.

Comcast seems to have decided to unilaterally change things without bothering to tell anyone.

[walts48]

Don't know where I wasn't being patient. More surprised that I wasn't seeing more reports of the problem.

There are over 25 million Thunderbird users. Surely there are more than the now 5 users reporting the problem using Thunderbird with Comcast POP. Maybe not.

Not a mention of the problem in the m.support.thunderbird newsgroup, Only one on the mozillaZine forum (tomdkst's post), none on reddit. Didn't check Thunderbird support at SUMO.

I have my Thunderbird betas on Ubuntu and Linux Mint switched over to IMAP.

May try csheppner's workaround on my Ubuntu supplied 60.2.1.

Undecided about my 60.3.1 and 65.0a1 versions from Thunderbird.

[james-warner]

Allow me to join this growing crowd as I've experienced the same problem since last Sunday. I am running Thunderbird 60.2.1 64-bit under Ubuntu 18.10. For what it's worth my experience suggests the root cause is somehow related to Ubuntu, possibly systemd-resolved.

With the same resources (router, ~/.thunderbird directory contents, etc) I experience no problem running Thunderbird 60.3.0 under Fedora-29, openSUSE Tumbleweed or an iMac. My pop3 email is retrieved from mail.comcast.net without problems.

I, too, wish to thank cscheppner for the work around.