Unable to send mails

hi everyone i used to send mails using ruby on rails but, all of a
sudden i am unable to send mails. the code is fine when i use the same
code in other systems i am able to send the mails.when it comes to my
system i'm not able to send it. can any one help me out what might be
the problem . i am using windows os my rails 2.3.8 and ruby version
1.8.7

Thanks in advance guys