I need to determine if the ISP is blocking or closing a local port? 2

[dogrofflog]

I need code to determine if port 25 is being blocked by the ISP (or any other program like that).

Thats it! Short and simple? I'll use any common ocx tha comes with VB6 if that works easy but maybe there is some solid API code out there (will work on 95,97, 2000, xp) that will get the job done too!

Thanks in advance!

 

[chiph]

Port 25 is the STMP (email) port. Please don't tell us you plan on sending spam.

The only way to find out is try to send something on it. They're help desk won't be able to tell you (ISP help desks are usually staffed with reboot monkeys).

Chip H.


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[dogrofflog]

No, we dont plan on spamming. We are 100% can spam compliant and we encourage our clients to send out valid emails to their clients.

I need a diagnostic utility to help us dertermine sending problems on our clients machine and a locked port 25 is pretty standard in many isps. If it's blocked, then we have other solutions for them.

Thanks,
Still waiting on some good code here!

 

[Sheco]

Well why don't you use the winsock control to try to connect on port 25?

Maybe set up a host on your side to be the test recipient and that way, if your users can connect to you then you will know they can get through.

 

[dogrofflog]

Yeah, that's kinda what I thought but I thought I'd throw it out there and see if any odeas pop up beyond the winsock control.

There has to be some kind of API or something I thought to check the status of ports but I guess it's more, can data get through that port or not kinda deal.

Thanks for your help guys!

 

[Sheco]

Yes you can do it with the API, using the control is just a shortcut.

 

[dogrofflog]

Right... so.... you wouldn't happen to have the API code readily available or a website somewhere with the sample code.....


laziness has set in here

 

[Sheco]

Not here at work ...

Take a look at this web page:

http://www.vbip.com/winsock-api/

I think it will have everything you need. If not let me know and I see if I can't dig up the CD for an old ftp thingy that I made at a previous job.

 

[dogrofflog]

I'll take that! Thanks amigo!

 

[dilettante]

Gosh, why not just Telnet out on port 25 to a known mail server somewhere?

 

[dogrofflog]

will do amigos!

wish there was away I could tell WHY, firewall, isp blocked port, as to reason when it would fail telnetting out of port 25.

Thanks again guys!

 

[dilettante]

Hmm... none of these may do you any good. I just tried some tests from home (Comcast) and I find that even if I try bogus DNS locations on 25 I get connected to "AVG ESMTP Proxy Server" so there are more tricks in the ISP bag than port blocking these days.

 

[Sheco]

So they were redirecting all port 25 traffic to their proxy server?

 

[dilettante]

I even tried sending mail to "fake.com" and this monster grabbed it.

I captured the port 25 traffic and the server plays nice, makes the client think everything went ok, but the mail message was blackholed and not sent on to the recipient.

 

[dilettante]

That's got to be it Sheco, I've tried several known external mail servers on 25 and they all get redirected to this proxy.

 

[dogrofflog]

No kidding. They are getting sneaky. IT MAKES my techsupport life a NIGHTMARE let me tell you!

Hey, any more digging into this would be great! I am so swamped with other stuff (just getting our new software up and running)

http://www.ntesoft.com

That is very interesting testing. Thanks so much for looking into this as much as you already have!

 

[Sheco]

Can you "talk" to the port 25 proxy like a regular mail server?

I mean if you telnet to on port 25 to mail.fake.com will it prompt you just like a mail server? Can you start talking to it as if you were a mail client ... ie: HELO fake.com

 

[dogrofflog]

AVG, isn't that the antivirus program from grisoft.com?

interesting, so if they redirect to a proxy server and let the proxy handle it, there's no way to know if they will allow it out or not is there?

 

[Sheco]

The proxy probably just limits the number of messages that can be sent from a particular sender over a particular period of time.

It might also be scanning for email virii and reading your mail. eek!

 

[Sheco]

dogrofflog you can maybe set up a host server on your end... have the client send you an email, if it gets through then great, even if it goes through a proxy who cares if it got through.