On Thu, 4  Mar 1993 07:18:24 PST  Glee Willis <[log in to unmask]>
said:
 
>I "walked"  Nathan through a  port 25 inquiry,  showing how he  would be
>able  to simultaneously  obtain the  host _name_  equivalent for  the IP
>number he was  using, as well as  verify the existence of  the userid in
>question which, FWIW, *does* exist.
 
Don't trust what VRFY  says. Oh, if it says the  user doesn't exist, then
it very  probably doesn't, but if  it replies positively it  doesn't mean
anything. SMTP may not  be in a position to know  whether the user really
does exist, as  it may just be  an "input channel" into  an external mail
system. Thus,  it is  not required  to verify  that the  mailbox actually
exists, only  to say whether  it will accept a  message for that  user or
not. The message can later be rejected by another mailer down the path.
 
  Eric