Author Topic: SMTP to a clustered server not working  (Read 47 times)

timberbt

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SMTP to a clustered server not working
« on: April 24, 2018, 02:38:42 PM »
Hi, one of our vendors uses Chilkat to send SMTP messages and I'm trying to troubleshoot an issue.   

We have an SMTP relay used throughout our company that works just fine for all other applications referencing the SMTP server by name.   There is a cluster/load balancer going on so if you do an NSLOOKUP on that it returns 3 addresses.

From the server in question I can manually connect and send email to each of the 3 addresses SMTP servers with no issue.

In the client application that sends using Chilkat, if we put in any of the 3 IP Addresses directly it works.   However if I provide the host name it will not send.   I don't get a lot of visibility inside their software and logging is next to nothing, except to say that it failed.

Version on their DLL is shown as 9.3.1.0 (ChilkatDotNet4.dll)

Is there an issue here about resolving the SMTP endpoint when multiple addresses are returned?   

NSLookup output looks like this: (addresses and names changed to protect the innocent)

Code: [Select]
C:\>nslookup smtprelay.mycompany.com
Server:  globaldns1.mycompany.com
Address:  52.38.140.2

Non-authoritative answer:
Name:    smtprelay.mycompany.com
Addresses:  52.38.140.53
          52.38.140.54
          52.38.140.55