Question : 550 Sender verify failed

We are having trouble sending mail to an entire domain, and coincidentally, that domain is unable to send us mail.

Our mail server is hosted with GoDaddy.com (who uses a mail server at secureserver.net). Our domain name is mcgrailgroup.com.

The intended recipient domain is ccil.org. I have masked the sender and recipient addresses for privacy reasons.

When I send an email from mcgrailgroup.com to ccil.org, I get the following bounceback:

Hi. This is the qmail-send program at smtpout03-04.mesa1.secureserver.net.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

:
192.190.237.100 does not like recipient.
Remote host said: 550-Verification failed for
550-Called:   64.202.166.12
550-Sent:     RCPT TO:om>
550-Response: 553 192.190.237.* rejected due to spam, contact 480-505-8877 (Attack detected from pool 192.190.237.216)
550 Sender verify failed
Giving up on 192.190.237.100.

When I send an email from ccil.org to mcgrailgroup.com, I get the following bounceback:

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

[email protected]
SMTP error from remote mailer after RCPT TO:om>:
host smtp.secureserver.net [64.202.166.12]: 553 192.190.237.* rejected due
to spam, contact 480-505-8877 (Attack detected from pool 192.190.237.216)

----------

I know GoDaddy does extensive spam filtering, but this is unexplainable as far as I can figure that both sender and receiver would get the same error messages.

Answer : 550 Sender verify failed

Ok first lets break down the mail to ccil.org.

192.190.237.100 does not like recipient.
Remote host said: 550-Verification failed for
550-Called:   64.202.166.12
550-Sent:     RCPT TO:om>
550-Response: 553 192.190.237.* rejected due to spam, contact 480-505-8877 (Attack detected from pool 192.190.237.216)
550 Sender verify failed
Giving up on 192.190.237.100.

Notice the 550-Sent:    RCPT TO:m>

This is an address in your domain, not ccil.org.  If you were sending a message to ccil.org it should RCPT TO a ccil.org address.  From the rest of the
message it appears that once you connect to their mail server and issue MAIL FROM:.com>, their mail server then connects back
to smtp.secureserver.net (your hosting provider) and issues a RCPT TO for the mail address you are sending from.  Likely this is a step their mail server
uses to verify the sender before allowing the message to be accepted (antispam measure).  When it issues the RCPT TO it receives the 553 error and
disconnects.  This then causes your message to fail.

Now when they send to you:

[email protected]
SMTP error from remote mailer after RCPT TO:om>:
host smtp.secureserver.net [64.202.166.12]: 553 192.190.237.* rejected due
to spam, contact 480-505-8877 (Attack detected from pool 192.190.237.216)

This rejects the message with the same error as the other one.  The message is the same because in both situations the ccil.org mail server is connecting
to smtp.secureserver.net and issuing a RCPT TO and getting a 553.  Now the $64,000 question, why is it rejecting?

Well look closely at the description:

553 192.190.237.* rejected due to spam, contact 480-505-8877 (Attack detected from pool 192.190.237.216)

The smtp.secureserver.net server appears to be on a subnet that is being categorically rejected by the secureserver mail server.
Notice it says 192.190.237.* which indicates that entire subnet (assuming regular class C mask) is being rejected.  Its possible that
secureserver.net has either rejected this IP block or its on a blacklist somewhere.

The only way to really know is to call the number in the NDR and find out.  Not much you can do from the client end to fix this that wouldn't end up
being an inconvenience.