Sendmail is not snding mail but giving dead.letter. What is dead.letter?

When ever I am trying to email through command line or through perl,
go the dead.letter issue.
Below is the output of Perl Script....
OutPut:
Hello
Processing email
/home/gsaxena/dead.letter... Saved message in /home/gsaxena/
dead.letter
Email closed

Hello is just a print // customized String
Processing email is written before open mail command // customized
String
/home/gsaxena/dead.letter... Saved message in /home/gsaxena/
dead.letter is the issue // Not able to send email
Email closed is just a print // customized String

Please suggest.

Thanks,
Gaurav

 

"dead letter" is a term used in the real Post Office, and refers to mail
that can not be delivered - often because the address is wrong, or there
is no stamp, and no (useful) return address. SMTP uses a similar function
when email is undeliverable for any reason.

Mail configuration problem. Look in /var/log/maillog for clues. There
are just to many possible causes to guess what the problem may be, but
it usually revolves about addresses - destination address is bad, no
working DNS to locate a mail server at the destination, blocklist
problems where the destination refuses to accept your mail, sender is
not accepted by the destination... really a lot of things.

Old guy