"Failure sending Mail" error on program

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 开发者_运维技巧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.

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.

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.