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my friend gave me a program which runs in his laptop, he coded with system.webmail and C#, that program can send the email in his machine, but when i run and send it out in my machine, the email didn't send and get "Failure Sending Mail", but in his computer, he can send with his internet. But I am still getting error, even i can't ping to SMTP server or telnet. What will be issue, does my ISP ban the port, or ISP firewall ban the port?

I use port 25 and also 587 too. but it doesn't do any different at all.

XML guy
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  • It's probably a configuration issue. Does his program try to send the e-mail through a local SMTP server on his machine, or a remote server? It could be any number of things, so additional information would be helpful. – Tim Aug 04 '11 at 18:33
  • the remote server (SMTP.LIVE.COM) along with authentication; the configuration is fine too. It works in his network (Singapore), but that doesn't work in my PC (US). – XML guy Aug 04 '11 at 18:35
  • Are you able to authenticate to the server? Do you have the source code? – Tim Aug 04 '11 at 18:38
  • Are you running any virus checkers or firewalls on your PC? Have a look at this http://stackoverflow.com/questions/3194978/prevent-anti-virus-to-block-outgoing-email-with-c – John Aug 04 '11 at 18:39
  • Yes, in his network (Singapore), it authenticates and works, but when i use it in my network(US), i am getting this failure error. – XML guy Aug 04 '11 at 18:40
  • No, I don't use any anti-virus or firewalls at home. – XML guy Aug 04 '11 at 18:41

2 Answers2

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There is an unfixed bug in System.Mail.SmtpClient where sending mail to a domain-enabled (Exchange) server fails if you cannot domain authenticate, even if username and password would authenticate, but only if you are farther than ~10ms from domain server.

Joshua
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I have a same issue before and it turned out that the email provider "Smart Mail" is blocking my email, The solution I simply added the email address at the safe list in my destination email.

Jalal Said
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  • well, i am sending mail to same address as sender email address. in my case, this may not be issues. – XML guy Aug 04 '11 at 18:58