Aug 14 09:24:53 test sendmail[22190]: v7E9OrwY022190: to=nsd@gmail.com, ctladdr=www-data (33/33), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30133, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (v7E9OrUd022191 Message accepted for delivery)
Aug 14 09:24:53 test sm-mta[22193]: STARTTLS=client, relay=gmail-smtp-in.l.google.com., version=TLSv1.2, verify=FAIL, cipher=ECDHE-RSA-AES128-GCM-SHA256, bits=128/128
Aug 14 09:24:53 test sm-mta[22193]: v7E9OrUd022191: to=<nsd@gmail.com>, ctladdr=<www-data@test.wt> (33/33), delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=120375, relay=gmail-smtp-in.l.google.com. [64.233.166.27], dsn=5.6.0, stat=Data format error
Aug 14 09:24:53 test sm-mta[22193]: v7E9OrUd022191: v7E9OrUd022193: DSN: Data format error

<?php
mail ("nsd@gmail.com","sdfsdfs",
             "xdgsdgs","nsd@gmail.com");
?>

root@test:~# telnet 127.0.0.1 25
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 test.wt ESMTP Sendmail 8.15.2/8.15.2/Debian-3; Mon, 14 Aug 2017 09:41:50 GMT; (No UCE/UBE) logging access from: localhost.localdomain(OK)-localhost.localdomain [127.0.0.1]

helo server
250 test.wt Hello localhost.localdomain [127.0.0.1], pleased to meet you
MAIL from:nsd@gmail.com
250 2.1.0 nsd@gmail.com... Sender ok
RCPT to:nsd@gmail.com
250 2.1.5 nsd@gmail.com... Recipient ok
DATA
354 Enter mail, end with "." on a line by itself
Subject: ndfgjkd
from:nsd@gmail.com
to:nsd@gmail.com
Test Mail
.
250 2.0.0 v7E9fo40022316 Message accepted for delivery

127.0.0.1 localhost.localdomain localhost
127.0.1.1 test.wt

# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts