mx gmail.com accept and rejects?

Question

can somebody explain such behavior of gmail?

root@mx0:# telnet gmail-smtp-in.l.google.com 25
Trying 173.194.71.26...
Connected to gmail-smtp-in.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP f7si526563lbe.161 - gsmtp
QUIT
221 2.0.0 closing connection f7si526563lbe.161 - gsmtp
Connection closed by foreign host.

root@mx0:# telnet 176.9.118.232 25
Trying 176.9.118.232...
Connected to 176.9.118.232.
Escape character is '^]'.
Connection closed by foreign host.

root@mx0:# telnet mx.google.com 25
Trying 176.9.118.232...
Connected to mx.google.com.
Escape character is '^]'.
Connection closed by foreign host.

???

Where are you getting the IPs from? – ceejayoz Jul 22 '13 at 19:44 — ceejayoz, Jul 22 '13 at 19:44
Is there a specific issue that you're experiencing? – Nathan C Jul 22 '13 at 19:50 — Nathan C, Jul 22 '13 at 19:50

score 1 · Answer 1 · answered Jul 22 '13 at 19:53

The mx.google.com and 176.9.118.232 are obviously the same IP address, while gmail-smtp-in.l.google.com is not the same.

There could be multiple reasons this doesn't work, but first and foremost, I would venture to guess that it is secured. Just because one of their SMTP servers accepts requests at port 25 unsecured doesn't mean that they all will. In fact, when I look up their MX servers through a simple NSLOOKUP, I do not get mx.google.com. It could be that it isn't a mail server at all or even doesn't exist all together.

score 0 · Answer 2 · answered Jul 22 '13 at 20:01

[~] host mx.google.com
Host mx.google.com not found: 3(NXDOMAIN)


[~] host 176.9.118.232
232.118.9.176.in-addr.arpa domain name pointer master.rejector.ru.

your dns is broken.(or has some sort of wild card for NXDOMAIN which to me is broken). mx.google.com doesn't exist, you are hitting something that isn't google. Now why you are trying to go to mx.google.com is another story. mx's are returned from DNS queries for 'mx' type records. There is no requirement to have a host named mx.

-edit-

Ahh I see the server ids it self as mx.google.com. That is just the hostname of the server. It doesn't have to exist globally, or even be valid. It is best practice for that hostname to exist and match the ptr of the ip when sending email,but upon receiving email it isn't used for anything.

Thank you Don, forgot about PTR check :) It's DNS filter – user182619 Jul 22 '13 at 20:29 — user182619, Jul 22 '13 at 20:29

mx gmail.com accept and rejects?

2 Answers2