SMTP Problem - Exchange + Outlook

We have not had any issues with our exchange server in the past but the users are now trying to contact a new email client and are receiving an error message - see below:
"There was a SMTP communications problem with the recipient's email server. Please contact your system administrator. <exchange server name.domain #5.5.0smtp;554. This server requires PTR for unauthenticated connections.>"
I have contacted our ISP and they have added an "A" record in our DNS list pointing to the name of the exchange server.domain and the routable IP address assigned to the exchange server. We still get the same error message. What would I require to do to be able to send email?
GeneratorAsked:
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Alan HardistyConnect With a Mentor Co-OwnerCommented:
Has your ISP added a Reverse DNS record to your fixed IP Address?

Check your IP Address on www.blacklistalert.org (result should show any issues at the top of the results for your IP Address).
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Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
Some external domains do check for your PTR and if it doesnt get then it would reject your emails.

Also check
www.mxtoolbox.com 

Check inbound and outbound email
www.exrca.com

- Rancy
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Charlie2012Connect With a Mentor Commented:
You need to get the reverse DNS record set up.

It would look something like this:

name ttl  class   rr     name
15         IN     PTR    www.example.com.


TTL 2d ; 172800 secs
$ORIGIN 0.168.192.IN-ADDR.ARPA.
@             IN      SOA   ns0.example.com. mailmaster.example.com. (
                              2003080800 ; serial number
                              12h         ; refresh
                              15m        ; update retry
                              3w         ; expiry
                              3h         ; minimum
                              )
              IN      NS      ns0.example.com.
              IN      NS      ns1.example.com.
; 2 below is actually an unqualified name and becomes
; 2.0.168.192.IN-ADDR.ARPA.
2             IN      PTR     hello.example.com. ; FDQN
....
15            IN      PTR     www.example.com.
....
17            IN      PTR     goodbye.example.com.
....
74            IN      PTR     daisy.example.com.

There are many PTR record checking tools to make sure you have this set up correctly. When you asked your ISP for the DNS entry did you specify a PTR to point to your MX record?:

http://www.webmaster-toolkit.com/ns-lookup.shtml
....
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GeneratorAuthor Commented:
We have added the PTR record for mail.example.com (used our credentials) and all the tests are successful indicating that the reverse DNS is working properly. However, the same error message still shows up when emailing that one client. Since the error message points to the name of the exchange server (exc-01.domain name) directly, should we also add a PTR record pointing to the name?
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Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
No the PTR should ideally be the MX entry ... and i guess your Firewall\Gateway server is the incoming and outgoing server .....

- Rancy
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Alan HardistyCo-OwnerCommented:
If you run the following from a command prompt - do you see mail.example.com as the result:

nslookup your_external_ip_address (e.g., nslookup 123.123.123.123)
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GeneratorAuthor Commented:
If the solution to the question is found by the asker - how would one close the question without points being awarded? I have found the answer to questions before and noted the results in my comments but the question remained open. The only way to close the question seems to be picking one responder and awarding him the points.
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GeneratorAuthor Commented:
OK - thanks
Please award the points as you see fit.
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