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QuestionSMTP Programming PinmemberDisIsHoody9-Dec-12 14:49 
Let me start off by saying that I apologize in advanced if this isn't the correct forum for this question, but there didn't seem to be a forum that exactly matched the question/issue I'm having.
 
I'm a VB.NET developer and I like to expand by knowledge by trying to program things from scratch that are already implemented ih the.NET framework. My current project is programming a SMTP server using just sockets. I've already read the RFC on SMTP and my company has an Exchange Server (2007) that I was going to use for testing.
 
The web address of the server is exchange.mycompany.com and I used reverse DNS to get the IP adress. The domain name does have a MX record a well. From the command prompt on my computer (which is running Win7 Professional) I tried using telnet to connect on port 25. I tried using the domain name as well as the IP address, but both times it said it couldn't connect to the server on port 25.
 
I checked the settings ih Outlook and the port is correct. I then tried connecting on port 110, and some other ones that are sometimes used, and it gave the same error message.
 
Next I connected to the Exchange server through VPN and tried telnet again on port 25 and this time it worked. However in the SMTP banner it said remote.mycompany.com instead of exchange.mycompany.com. So I disconnected from the VPN and tried the telnet again on all the ports I initially tried but used remote.mycompany.com but again got the same error message. I did an IP address lookup and remote.mycompany.com and exchange.mycompany.com point to the same IP address.
 
I then used mxtools.com and dnsstuff.com (I think that was the adress) and used their SMTP tools to see of they could connect. I entered mycompany.com as the domain name and they looked up the MX record, which returns exchange.mycompany.com as the SMTP server, and both tools were able to connect with no issues identified.
 
So my questions: 1) If the MX record list exchange.mycompany.com as the SMTP sever, why does the banner return remote.mycompany.com? 2) Why can't I connect the SMTP server through telnet unless I'm connected through VPN, but the two websites I used to test it the connection worked?
 
Obviously the server works because because the two websites can connect to it, I can when I'm in VPN, and other servers can because I receive email on my corporate account. What could prevent my computer from connecting to the SMTP server through telnet when I'm not on VPN. I should also mention that I even tried turning off all my anti-virus software to make sure that it wasn't blocking it.
 
Any help would be greatly appreciated since I assuming if I can't telnet in I most likely wouldn't be able to connect through sockets so I can't start working on my project until I solve this.
 
Thanks,
 
Dominick
AnswerRe: SMTP Programming Pinmembervbmike10-Dec-12 9:49 
GeneralRe: SMTP Programming PinmemberDisIsHoody10-Dec-12 14:30 
GeneralRe: SMTP Programming PinmvpRichard MacCutchan10-Dec-12 22:36 
GeneralRe: SMTP Programming PinmemberDisIsHoody11-Dec-12 10:40 
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GeneralRe: SMTP Programming PinmemberDisIsHoody11-Dec-12 11:44 
GeneralRe: SMTP Programming PinmvpRichard MacCutchan11-Dec-12 11:58 
GeneralRe: SMTP Programming PinmemberDisIsHoody11-Dec-12 12:20 
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