Help needed sending emails to certain domains. Maybe blacklisted?

We had a problem where our server was compromised and got opened up as a relay.  This problem is now corrected but I have multiple issues in the aftermath of it.  

We have emails that go out and we the receiver get the email, it falls into their SPAM folder and it never did this before.  I'm referring to companies we had regularly emailed and still do.

We still have some domains that we can't email to.  It appears as if we are blacklisted.  See below.

Diagnostic information for administrators:
Generating server: VENUS.LOCAL.iob-gso.com
ourfriend@att.net
flpd599.prodigy.net #553 5.3.0 flpd599 DNSBL:RBL 521< 64.196.118.65 >_is_blocked.For information send an email to abuse_rbl@abuse-att.net ##
Original message headers:
Received: from VENUS.LOCAL.iob-gso.com ([2002:8101:129::8101:129]) by
 VENUS.LOCAL.iob-gso.com ([2002:8101:129::8101:129]) with mapi id
 14.03.0224.002; Thu, 27 Oct 2016 08:23:03 -0400
From: <me@iob-gso.com>
To: <ourfriend@att.net>
Subject: testing email
Thread-Topic: testing email
Thread-Index: AdIwTNeRRCDp2AW+SQS/8yyg2YSiwg==
Date: Thu, 27 Oct 2016 12:23:02 +0000
Message-ID: <0CBB5438ADF6E84A9BBA55FA82B6818029C7CD10@VENUS.LOCAL.iob-gso.com>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach: yes
X-MS-TNEF-Correlator:
x-originating-ip: [192.168.100.67]
x-exclaimer-md-config: 4b845ab1-925f-41d0-a654-2ab6c1ae37e6
Content-Type: multipart/related;
      boundary="_004_0CBB5438ADF6E84A9BBA55FA82B6818029C7CD10VENUSLOCALiobgs_";
      type="multipart/alternative"
MIME-Version: 1.0

I have requested to be unblocked several times but to no avail.  I am unsure of where to go with these problems.

Thanks so much!

Lanee
Lanee KirbyAsked:
Who is Participating?
 
KimputerConnect With a Mentor Commented:
For these "problem" domains, you sadly have to find a trustworthy SMTP relay and forward to that relay. When you're finally removed from their blacklist, you can one by one turn off the relay (easiest way is to add the smtp relayer as the mx record for that domain on your own DNS server)
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Spencer SchererConnect With a Mentor Systems AdministratorCommented:
Additionally, you can also set your Exchange server to only relay emails that are going to a particular domain so that you limit the amount of emails you send through the relay as many times they have price points and limits for each level.  Very easy to setup and also remove once you get removed from the blacklist.
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Dr. KlahnConnect With a Mentor Principal Software EngineerCommented:
You're correct. AT&T has blacklisted you and given their unimpressive support it will probably stay that way for some time.  Unfortunately it's impossible to tell if it's this particular sending email address, or the IP address that the SMTP originator is on, or the IP block that the SMTP originator is in, or the domain name of the sending email address, or the domain name of the sending SMTP originator.  The issue could be any or all of the above.

I agree with Kimputer.  For some domains you'll have to send email through a trusted outgoing relay until the problem goes away.  If you sign up with a service such as SMTP2GO (which, full disclosure, I personally use), you can relay 5000 emails per month for $90 a year.  This is less than the cost of one hard drive and given that your emails are not going through, there should be no argument about the price.
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Dr. KlahnPrincipal Software EngineerCommented:
EE requested stale question closure.  All answers supplied are correct and useful.
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