Home/ Questions/Q 7561797
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-30T13:14:57+00:00

I’m trying to open a socket to a website over the Internet, but can’t.

  • 0

I’m trying to open a socket to a website over the Internet, but can’t. After about a minute, a ConnectException is thrown saying that the operation timed out.

Socket clientSocket = new Socket(InetAddress.getByName("gmail.com"), 25);

My computer is connected to a router, which is connected to the Internet. My router is configured to direct all incoming port 25 data to port 2550 on my local machine (192.168.2.2). So, I thought maybe if I set the “local address” and “local port” parameters on the Socket constructor it might work…but this also gives me an “operation timed out” error.

Socket clientSocket = new Socket(InetAddress.getByName("gmail.com"), 25, InetAddress.getByName("192.168.2.2"), 2550);

I saw this SO question, but was wondering if anyone could shed any more light on the issue. Thanks.

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    You are trying to connect to port 25 on gmail.com, but that machine is not an email server. You must first look up the MX record for gmail.com, and then try to connect to one of the delivery servers mentioned in the returned MX record.

    For example, with dig mx gmail.com on my machine, I get:

    ; <<>> DiG 9.3.6-P1-RedHat-9.3.6-16.P1.el5 <<>> mx gmail.com
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34063
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 4, ADDITIONAL: 4

;; QUESTION SECTION:
;gmail.com.                     IN      MX

;; ANSWER SECTION:
gmail.com.              1697    IN      MX      30 alt3.gmail-smtp-in.l.google.com.
gmail.com.              1697    IN      MX      40 alt4.gmail-smtp-in.l.google.com.
gmail.com.              1697    IN      MX      5 gmail-smtp-in.l.google.com.
gmail.com.              1697    IN      MX      10 alt1.gmail-smtp-in.l.google.com.
gmail.com.              1697    IN      MX      20 alt2.gmail-smtp-in.l.google.com.

;; AUTHORITY SECTION:
gmail.com.              266895  IN      NS      ns1.google.com.
gmail.com.              266895  IN      NS      ns2.google.com.
gmail.com.              266895  IN      NS      ns3.google.com.
gmail.com.              266895  IN      NS      ns4.google.com.

;; ADDITIONAL SECTION:
ns1.google.com.         262525  IN      A       216.239.32.10
ns2.google.com.         262525  IN      A       216.239.34.10
ns3.google.com.         262525  IN      A       216.239.36.10
ns4.google.com.         262525  IN      A       216.239.38.10

;; Query time: 65 msec
;; SERVER: 144.52.10.15#53(144.52.10.15)
;; WHEN: Tue Feb 28 14:30:04 2012
;; MSG SIZE  rcvd: 295

    So try connecting to port 25 on gmail-smtp-in.l.google.com (which is the server with the lowest MX priority number).

    • 0