# port 25 **URL:** \ **Category:** Factual Questions\ **Created:** [January 20, 2001, 11:02pm UTC](https://boards.straightdope.com/t/port-25/51068 "2001-01-20T23:02:34Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![cykrider](https://avatars.discourse-cdn.com/v4/letter/c/f19dbf/32.png) [@cykrider](https://boards.straightdope.com/u/cykrider)\ **Post date:** [January 20, 2001, 11:02pm UTC](https://boards.straightdope.com/t/port-25/51068/1 "2001-01-20T23:02:34Z")
Ok, I want to be able to telnet into an address and get in port 25. I’ve done this to some sites, but when I try and send myself an email, it says it can’t relay it because my ip address is possibly forged. I’m on a university LAN so my IP is dynamic. Is there any way I can send an annonymous email to myself if I have a dynamic IP? Where can I find other places to telnet into? I only know a few addresses. ---
**Author:** ![Bobort](https://avatars.discourse-cdn.com/v4/letter/b/ac8455/32.png) [@Bobort](https://boards.straightdope.com/u/Bobort)\ **Post date:** [January 21, 2001, 12:29am UTC](https://boards.straightdope.com/t/port-25/51068/2 "2001-01-21T00:29:03Z")
Any mail server that allows you to do this is called an open relay. Open relays are the primary obfuscation mechanism used by spammers (since they can send mail through open relays without their service provider noticing) and because of this network admins are strongly encouraged to configure their mail servers so as not to allow it. That’s why they’re in short supply. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [January 21, 2001, 12:56am UTC](https://boards.straightdope.com/t/port-25/51068/3 "2001-01-21T00:56:09Z")
To expand on **Bobort** ’s post, properly configured mail servers will only accept outgoing mail from an IP on the same network as the mail server. The mail server at my school, for example, will only accept outgoing mail from an IP that is part of the school LAN. ---
**Author:** ![Lord\_Jim](https://avatars.discourse-cdn.com/v4/letter/l/ecccb3/32.png) [@Lord\_Jim](https://boards.straightdope.com/u/Lord_Jim)\ **Post date:** [January 21, 2001, 4:11am UTC](https://boards.straightdope.com/t/port-25/51068/4 "2001-01-21T04:11:07Z")
I’ve had to deal with having an open relay mail server that a spammer discovered. It wasn’t fun. One has to wonder why you are looking for a server that you can telnet into and send yourself(?) some email. Especially after asking about [port sniffers](http://boards.straightdope.com/sdmb/showthread.php?threadid=55788) > [@](#): > > What exactly is a port sniffer? How does it work, and can one be coded in a high-level language such as C++ or something? and [c plus plus question](http://boards.straightdope.com/sdmb/showthread.php?threadid=56220) > [@](#): > > Is it possible to ping another computer using c++ and save the results in a text file or something? This isn’t a very good place to try to learn to be a hacker or a spammer. Jim ---
**Author:** ![cykrider](https://avatars.discourse-cdn.com/v4/letter/c/f19dbf/32.png) [@cykrider](https://boards.straightdope.com/u/cykrider)\ **Post date:** [January 21, 2001, 5:31am UTC](https://boards.straightdope.com/t/port-25/51068/5 "2001-01-21T05:31:32Z")
Although most of my questions may seem to be about hacker-topics I would like you to know that my questions are merely for a educational value. I’ve just started college and I’m interested in majoring in System’s analysis. I’m really into programming, but have little experience in networks and the such. Most of this “hacker” stuff doesn’t really make sense to me and so I ask questions. If I try anything a bit “hackerish” it’s going to be on myself and just to see how it works. I’ve been told this is the easiest and best way to learn. Right now I’m thinking about being a system’s administrator, if I don’t learn the in’s and out’s of system, I don’t think I’ll do a very good job. I can read about this stuff all day, but if I don’t try any of it, I’ll never learn anything. Right? I guess all you can really do is trust me on this one. But I have no intention of any malicious activities. Thanks for the concern though. If you know any better ways to learn, please feel free to share. ---
**Author:** ![Lynn\_Bodoni](https://avatars.discourse-cdn.com/v4/letter/l/e47c2d/32.png) [@Lynn\_Bodoni](https://boards.straightdope.com/u/Lynn_Bodoni)\ **Post date:** [January 21, 2001, 5:50am UTC](https://boards.straightdope.com/t/port-25/51068/6 "2001-01-21T05:50:09Z")
There is, or used to be, a newsgroup about tracking down spammers. I think it was N.A.N.A., News Announce Net Abuse. You might try them. ---
**Author:** ![Lord\_Jim](https://avatars.discourse-cdn.com/v4/letter/l/ecccb3/32.png) [@Lord\_Jim](https://boards.straightdope.com/u/Lord_Jim)\ **Post date:** [January 21, 2001, 6:04am UTC](https://boards.straightdope.com/t/port-25/51068/7 "2001-01-21T06:04:08Z")
Your explanation is fine with me, however I think you should understand that telling you how to find open relay mail servers is not a very good thing to be doing on this message board. Nor is telling you how to write a port sniffer program or log ping responses in C++. If I’m not mistaken, the entire Windows operating system is written in C++. So, if you are into programming, it should be obvious that you can do almost anything that a PC is capable of with C++. I’m sure if you looked around you’d find sites that would be happy to tell you that kind of stuff. If your questions are purely academic, I think you would agree that not everyone that has the capability of reading the responses to these types of questions are as above board as you are. Sorry, if I misread the intent of your line of questions. Jim ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [January 21, 2001, 6:20pm UTC](https://boards.straightdope.com/t/port-25/51068/8 "2001-01-21T18:20:07Z")
I do sympathise with you, **cykrider**. In the waaaaay back Dream-Time of the Net, when I was a younger lady, I tried to learn about all the same things you are, and even asked alarmingly similar questions. It is hard to get answers to them. One thing that helped a lot was getting involved in the FreeBSD/Linux community, since they are all open-source knowledge-sharing, and very open to discussing topics like port sniffers and mail spoofing, mainly because they look for ways to prevent unauthorized use of such tactics. This may be off-topic, but consider hanging out around there. Also think about setting up an old 486 or Pentium box as a Linux machine. You could learn a lot about the subjects you are interested in, and even be learning a skill which will convert to $$$ when you look for an IT job. ---
**Author:** ![TubaDiva](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tubadiva/32/507_2.png) [@TubaDiva](https://boards.straightdope.com/u/TubaDiva)\ **Post date:** [January 21, 2001, 8:27pm UTC](https://boards.straightdope.com/t/port-25/51068/9 "2001-01-21T20:27:36Z")
Please understand that while we’re all for the eradication of Ignorance, some topics are best left unexplored, at least on this board. There’s any number of places where this information can be found, both online and in reference material. Just my opinion here, but it also sounds like you’re trying to run before you can walk; that is, you’re attempting to find out about what interests you without having the underlying technological understanding that education brings. Get a good grounding first, learn the system basics, then all of this will make much more sense to you and you’ll not only get it but retain it and be able to use it. Even though your motives may be entirely benign, keep in mind that most people you encounter in cyberspace have had bad experiences with hackers/crackers/cyberjerks and anything that even smacks of that sort of mentality tends to get a negative response. your humble TubaDiva Adminstrator ---
**Author:** ![cykrider](https://avatars.discourse-cdn.com/v4/letter/c/f19dbf/32.png) [@cykrider](https://boards.straightdope.com/u/cykrider)\ **Post date:** [January 21, 2001, 9:44pm UTC](https://boards.straightdope.com/t/port-25/51068/10 "2001-01-21T21:44:22Z")
Thanks again for the concern. Actually Tuba that’s kind of what I’m trying to is get some basics, but every now and then I come across something that, like in this case, is thrown in with the rest of the “basics” and so it throws me off. I’ll watch what I post from now on. Since this thread I’ve run by [google.com](http://google.com) and found some other sites that are pretty helpful. I thank the SDMB for pointing me in the right directiong though…which is kinda what I wanted in the first place. Thanks guys. ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [January 31, 2001, 3:00pm UTC](https://boards.straightdope.com/t/port-25/51068/11 "2001-01-31T15:00:51Z")
I am almost positive this has been asked before. It should have anyway. I searched for “port address” in GQ and got back over 1600 threads. None of the first dozen or so were promising… Anyway, what are the ports doing exactly? AOL Instant Messenger will not work on the proxied network I have at work. But I have found that if I change the port setting really low, like 25, it _will_ work. Then, if I use a dial-up connection later, or plug back into my cable modem at home (we are talking a laptop here) I have to change the port setting back to 1000. It wont work at 25. Why is this? ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [January 31, 2001, 3:03pm UTC](https://boards.straightdope.com/t/port-25/51068/12 "2001-01-31T15:03:17Z")
Goddamn I am a retard… ignore this. And I apologize to whomever’s thread I just bumped to page two. BTW, the fact that this thread talks about Port 25 and I also used port 25 to connect to AOL IM, is merely a coincidence. But a strange one at that… is there something special about port 25 that I did not realize? ---
**Author:** ![Joe\_Cool](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Joe\_Cool](https://boards.straightdope.com/u/Joe_Cool)\ **Post date:** [January 31, 2001, 4:08pm UTC](https://boards.straightdope.com/t/port-25/51068/13 "2001-01-31T16:08:35Z")
Bear\_Nenno, I’m crossposting this to your thread also. > [@](#): > > \*Originally posted by Bear\_Nenno \* > \*\*…the fact that this thread talks about Port 25 and I also used port 25 to connect to AOL IM, is merely a coincidence. But a strange one at that… is there something special about port 25 that I did not realize? \*\* No. The something special is AIM’s login server (oscar). It listens on pretty much every commonly used port, specifically to make it easier for people to connect through firewalls. 5190 is the default AIM port, but it also listens on: 13: daytime 20: ftp data 21: ftp 23: telnet 25: sendmail 37: time 53: DNS 69, dudes! 70: gopher 79: finger 80: http 88: kerberos 110: pop3 113: authentication 119: nntp (USENET) 123: ntp (network time protocol) 137: netbios 8080: https and a whole mess of other ones. Basically, they set it up to make it as easy to connect as possible, which is a Good Thing®. A port is just an extension of your computer’s address. The IP tells data how to find the computer, and the port tells the data what service it needs to go to once it reaches that computer (sort of like the apartment number, vs. the street address). Port 25 is the address of the Unix Sendmail program, which is the mail relaying agent. Hope I’ve been helpful.