password Recovery controls throws email id of the user not existing error

I am using membership for mangaing user accounts in asp.net 2.0 application.
My password Recovery controls throws email id of the user not existing error
when button is clicked after given security answer.
actually this email is there, to which my application can send mail to the user.
I am using one external server for emailing ( the IP given is of external server), program tested from the hosting server (my application  can send mail from the above mail server, but cannot use
from password recovery control)

 what went wrong?

 
see my webconfig settings for mail settings

 
<system.net>
    <mailSettings>
      <smtp deliveryMethod="Network">
        <network host="<IP ADDRESS>" port="25" userName ="support" ...