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Suddenly getting Remote host said: 550 Invalid Sender [502]
Problem reported by Siraj Patel - March 24, 2015 at 12:06 AM
Submitted
Today, I suddenly started getting error messages when sending mail to my few set of email accounts. The rejection message is 550 Invalid Sender [502]". But it is totally random as to which user it happens to and when it happens.
 
This seems to happen with a specific extension emails only .ae all other emails are working fine, what could have gone wrong all of a sudden?
 
 

4 Replies

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0
Bruce Barnes Replied
March 24, 2015 at 12:44 AM
Post the SENDING DOMAIN name and we can run some external tests on your configuration.
Bruce Barnes
ChicagoNetTech Inc

Phone: (224) 444-0169

E-Mail and DNS Security Specialist
Network Security Specialist

Customer Service Portal: https://portal.chicagonettech.com
Website: https://www.ChicagoNetTech.com
Security Blog: http://networkbastion.blogspot.com/

Web and E-Mail Hosting, E-Mail Security and Consulting
0
Siraj Patel Replied
March 24, 2015 at 1:21 AM
Hi Bruce,
 
dmd.ae (SmarterMail Enterprise Edition, Version 11.3.4898) is one of the domain in the server sending mails to xyz@eim.ae (hosted elsewhere)
0
Bruce Barnes Replied
March 24, 2015 at 9:31 AM
If the recipient is doing a hard check for valid SPF, you will fail because you have no SPF record:
 
 
 
We check for INVALID SPF records, but pass if there is no SPF record.
 
 
You also have a NAMESERVER (DNS) issue:
 
You have TWO nameservers listed with your DOMAIN NAME registrar:
 

ns1.dubai-hosting.net. | No Glue | TTL=3600
ns2.dubai-hosting.net. | No Glue | TTL=3600

 
 
but the only DNS server which responds is ns1.dubai-hosting.net on 204.10.78.130
 
This could be caused by the fact that both of your DNS servers appear to be on the same IP ADDRESS.  DNS must be on different IP addresses and, for both redundancy and maximum availability, should be located on separate CLASS C subnets.
 
While this is, in and of itself, not a reason to bounce messages, it can be confusing to some mail servers and antispam checks and cause them to outright reject messages.
 
At least 2 (RFC2182 section 5 recommends at least 3), but fewer than 8 NS records exist (RFC1912 section 2.8 recommends that you have no more than 7).   This meets the RFC minimum requirements, but is lower than the upper limits that some domain registrars have on the number of nameservers.

A larger number of nameservers reduce the load on each and, since they should be located in different locations, prevent a single point of failure.

Hope this helps you troubleshoot your issues.
 
If you still have problems resolving the problem, you can either open a ticket with SmarterTools or contact one of the techs on here for paid troubleshooting and support.
Bruce Barnes
ChicagoNetTech Inc

Phone: (224) 444-0169

E-Mail and DNS Security Specialist
Network Security Specialist

Customer Service Portal: https://portal.chicagonettech.com
Website: https://www.ChicagoNetTech.com
Security Blog: http://networkbastion.blogspot.com/

Web and E-Mail Hosting, E-Mail Security and Consulting
0
Siraj Patel Replied
March 25, 2015 at 12:03 AM
the name servers are as below
 
ns1.dubai-hosting.net.   ['204.10.78.130']   [TTL=172800] 
ns2.dubai-hosting.net.   ['204.10.78.26']   [TTL=172800] 
 
and it has been working for so long without any issues, but just since yesterday the error has popped up.

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