Verizon seems to be blocking my smtp server
matthearn
Enthusiast - Level 1

Hello all!  I'm having issues sending mail using the email server provided by my webhosting company, and it seems as though Verizon is actually blocking port 465/tcp to it.  I'm aware that they globally block 25/tcp for non-static IPs, but until recently I had no problem reaching my mail servers on 465.  I can reach the gmail SMTP service:

homeserver> nc -vzw 3 smtp.gmail.com 465
Connection to smtp.gmail.com 465 port [tcp/urd] succeeded!

But not my personal one:

homeserver> nc -vzw 3 mail.hearntech.net 465
nc: connect to mail.hearntech.net port 465 (tcp) timed out: Operation now in progress

"homeserver" is a linux server on my router-attached network.  I also have an Amazon EC2 instance from which I can reach my mailserver, so I know it's not down:

amazonec2> nc -vzw 3 mail.hearntech.net 465
Connection to mail.hearntech.net 465 port [tcp/urd] succeeded!

I'm also able to send emails using my gmail account with no issues.

I don't believe that my webhost service is blocking me, but I'll be checking that too.  Does Verizon block certain mail destinations for some reason (suspected spam, maybe)?  Will I need to ask Verizon to remove the block, or might it clear on its own after a certain period?  Thank you!

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5 Replies
Cang_Household
Community Leader
Community Leader

May I ask what kind of service do you have? Residential or Business? For residential service, it is a violation of ToS to host web servers.

Otherwise, I would check the Firewall Log of your router. What kind of router do you have? I believe G3100's Firewall Logs cannot be retrieved correctly using the GUI. You may need to SSH into your router. For G1100, you should be able to see all the logs via the GUI.

matthearn
Enthusiast - Level 1

I was unclear; I have residential, but I'm not running web servers at home.  I use a hosting company (hostmonster, to be specific) to host multiple websites.  For example, I have hearntech.net; the SMTP server for it is mail.hearntech.net.  I know that port 465 is open on it because I can connect to it from outside my network, but can't connect from home.  I asked hostmonster to check and they say that my IP is not blacklisted.

I have a G1100; I checked the logs and only see inbound connections being blocked, nothing outbound.

Oddly, while I was chatting with a hostmonster technician, the ports suddenly became open, and then closed shortly afterwards.  Very odd behavior.

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Cang_Household
Community Leader
Community Leader

Maybe try a different computer to access the SMTP?

G1100 should not be blocking the port. You can see accepted inbound and outbound connections by turning on these logs in Firewall > Logs > Setting.

Can you use nmap to scan the SMTP port to see if it is reachable?

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matthearn
Enthusiast - Level 1

At the moment, ports are filtered, but of course I can't tell where or why:

╰ 09:20:53 $ nmap mail.hearntech.net

Starting Nmap 6.40 ( http://nmap.org ) at 2021-02-10 09:22 EST
Nmap scan report for mail.hearntech.net (67.20.114.55)
Host is up (0.060s latency).
rDNS record for 67.20.114.55: host2112.hostmonster.com
Not shown: 984 closed ports
PORT STATE SERVICE
21/tcp filtered ftp
22/tcp filtered ssh
25/tcp filtered smtp
26/tcp filtered rsftp
53/tcp open domain
80/tcp open http
110/tcp filtered pop3
143/tcp filtered imap
443/tcp open https
465/tcp filtered smtps
587/tcp filtered submission
993/tcp filtered imaps
995/tcp filtered pop3s
2222/tcp filtered EtherNet/IP-1
3306/tcp filtered mysql
5432/tcp open postgresql

Nmap done: 1 IP address (1 host up) scanned in 2.15 seconds

The above is from a virtual machine in my home network.  This is from an Amazon EC2 VM that's outside my home network:

14:23 $ nmap mail.hearntech.net

Starting Nmap 6.40 ( http://nmap.org ) at 2021-02-10 14:23 UTC
Nmap scan report for mail.hearntech.net (67.20.114.55)
Host is up (0.040s latency).
rDNS record for 67.20.114.55: host2112.hostmonster.com
Not shown: 984 closed ports
PORT STATE SERVICE
21/tcp open ftp
22/tcp open ssh
25/tcp filtered smtp
26/tcp open rsftp
53/tcp open domain
80/tcp open http
110/tcp open pop3
143/tcp open imap
443/tcp open https
465/tcp open smtps
587/tcp open submission
993/tcp open imaps
995/tcp open pop3s
2222/tcp open EtherNet/IP-1
3306/tcp open mysql
5432/tcp open postgresql

Nmap done: 1 IP address (1 host up) scanned in 1.78 seconds

Something's blocking me, I have no idea where, and it's annoyingly intermittent.  Sometimes I'm able to connect to 465.  I was able to connect to the ssh port earlier today, but right now it's blocked.  I am really starting to suspect my hosting service (there are other things going on over there that make me suspicious), but have no useful proof.

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Cang_Household
Community Leader
Community Leader

Can you try Release your DHCP and obtain a new IP address?

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