I have a form on a webpage that sends an email using sendmail on the same server. The recipient is a client that uses Google Apps for their email. In the form, I enter my email address. If I enter **\*@aol.com** or **\*@yahoo.com** (where "\*" is anything, not a literal asterisk, of course), the email fails to send with the following dump in `/var/log/mail.log`:

```
Sep 22 14:01:12 localhost sendmail[16522]: t8ME1CSU016522: Authentication-Warning: localhost.local: www-data set sender to no_reply@robwilkerson.org using -f
Sep 22 14:01:12 localhost sendmail[16522]: t8ME1CSU016522: from=no_reply@robwilkerson.org, size=1099, class=0, nrcpts=1, msgid=<201509221401.t8ME1CSU016522@localhost.local>, relay=www-data@localhost
Sep 22 14:01:12 localhost sm-mta[16523]: t8ME1CIi016523: from=<no_reply@robwilkerson.org>, size=1418, class=0, nrcpts=1, msgid=<201509221401.t8ME1CSU016522@localhost.local>, proto=ESMTP, daemon=MTA-v4, relay=localhost.local [127.0.0.1]
Sep 22 14:01:12 localhost sendmail[16522]: t8ME1CSU016522: to=recruitment@robwilkerson.org, ctladdr=no_reply@robwilkerson.org (33/33), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=31099, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (t8ME1CIi016523 Message accepted for delivery)
Sep 22 14:01:12 localhost sendmail[16527]: t8ME1CjK016527: Authentication-Warning: localhost.local: www-data set sender to no_reply@robwilkerson.org using -f
Sep 22 14:01:12 localhost sendmail[16527]: t8ME1CjK016527: from=no_reply@robwilkerson.org, size=1224, class=0, nrcpts=1, msgid=<201509221401.t8ME1CjK016527@localhost.local>, relay=www-data@localhost
Sep 22 14:01:12 localhost sm-mta[16528]: t8ME1CK4016528: from=<no_reply@robwilkerson.org>, size=1543, class=0, nrcpts=1, msgid=<201509221401.t8ME1CjK016527@localhost.local>, proto=ESMTP, daemon=MTA-v4, relay=localhost.local [127.0.0.1]
Sep 22 14:01:12 localhost sendmail[16527]: t8ME1CjK016527: to=marketing@robwilkerson.org, ctladdr=no_reply@robwilkerson.org (33/33), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=31224, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (t8ME1CK4016528 Message accepted for delivery)
Sep 22 14:01:13 localhost sm-mta[16530]: STARTTLS=client, relay=aspmx.l.google.com., version=TLSv1/SSLv3, verify=FAIL, cipher=ECDHE-RSA-AES128-GCM-SHA256, bits=128/128
Sep 22 14:01:13 localhost sm-mta[16525]: STARTTLS=client, relay=aspmx.l.google.com., version=TLSv1/SSLv3, verify=FAIL, cipher=ECDHE-RSA-AES128-GCM-SHA256, bits=128/128
Sep 22 14:01:13 localhost sm-mta[16530]: t8ME1CK4016528: to=<marketing@robwilkerson.org>, delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=121543, relay=aspmx.l.google.com. [173.194.205.27], dsn=5.0.0, stat=Service unavailable
Sep 22 14:01:13 localhost sm-mta[16530]: t8ME1CK4016528: t8ME1DK4016530: DSN: Service unavailable
Sep 22 14:01:13 localhost sm-mta[16530]: t8ME1DK4016530: to=<no_reply@robwilkerson.org>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=30000, relay=aspmx.l.google.com. [173.194.205.27], dsn=5.1.1, stat=User unknown
Sep 22 14:01:13 localhost sm-mta[16530]: t8ME1DK4016530: t8ME1DK5016530: return to sender: User unknown
Sep 22 14:01:13 localhost sm-mta[16530]: t8ME1DK5016530: to=root, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=30000, dsn=2.0.0, stat=Sent
Sep 22 14:01:13 localhost sm-mta[16525]: t8ME1CIi016523: to=<recruitment@robwilkerson.org>, delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=121418, relay=aspmx.l.google.com. [173.194.205.27], dsn=5.0.0, stat=Service unavailable
Sep 22 14:01:13 localhost sm-mta[16525]: t8ME1CIi016523: t8ME1DIi016525: DSN: Service unavailable
Sep 22 14:01:13 localhost sm-mta[16525]: t8ME1DIi016525: to=<no_reply@robwilkerson.org>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=30000, relay=aspmx.l.google.com. [173.194.205.27], dsn=5.1.1, stat=User unknown
Sep 22 14:01:13 localhost sm-mta[16525]: t8ME1DIi016525: t8ME1DIj016525: return to sender: User unknown
Sep 22 14:01:13 localhost sm-mta[16525]: t8ME1DIj016525: to=root, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=30000, dsn=2.0.0, stat=Sent

```

Every other email address that I've tried seems to work fine and the logs indicate success. Both seem to connect to the relay, but the failures fall apart right after that.

I can see that a service is unavailable, but I'm not entirely sure which one nor am I sure why it's only unavailable when I enter those addresses - especially when the sender is being forced to a `no_reply` email address. Why would the value I enter on the form matter at all? I'm clearly missing something.

I'm not a sysadmin and I'm certainly not well-versed in email troubleshooting so I'm hoping someone can give me a hand understanding what I'm looking at here. What could be causing these failures?