Server being rejected on mail deliver

[MateusVieira6740]

Hi,

i've tried to find a solution for this problem everywhere but i couldn't, so this is my last hope.
I'm a server admin and i have several clients hosted at my server, its a cpanel server, very common, one of my clients is trying to send messages to a domain using ironport cloud mail security system, but the messages keep being rejected.

The error from the log:

host mx1.hc4378-94.iphmx.com [68.232.140.15]

    SMTP error from remote mail server after DATA:

    550 #5.7.1 Your access to submit messages to this e-mail system has been rejected.

I even tried to contact CISCO with no lucky... 
The server's IP Address is not listed on any blacklists, i've used the Cisco Talos to check for the domain/ip reputation also, and its Good.

So i cannot understand why the system would block legitimate mail from our server.. 

Thanks

[shane.dollery]

Hi MateusVieira6740,
It sounds like the Sender IP is listed on a manual BLACKLIST by the recipient. If the recipients run Ironports then the sender IP is listed on the recipient's Public Listener BLACKLIST.

Regards,

Shane.

[MateusVieira6740]

Hi Shane, thanks for the answer.

To make sure i did understood what you said, this Blacklist is managed by the recipient running the Ironports, right.

Thanks for your help, again.

[shane.dollery]

Hi Mateus,
Yes, that's correct.
Regards,

Shane