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:
Code:
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:
Code:
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:
Code:
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!