Hi, I decided to setup a second email server in my company for POP3 purpose. My ServerA is a MS Exchange 2010 server with domainA.com. My ServerB is a POP3/IMAP server (smartermail) associated with domainB.com.
Both servers are on the same building but each has a different public IP. My router manages the two IP addresses and it is dispatching the TCP ports to the appropriate servers. The public address of domainB.com is 184.xxx.33.242.
Everything is working well except that my ServerA (MS Exchange, domainA.com) is incapable of sending emails to ServerB (smartermail, domainB.com).
ServerB receives all emails from everywhere I tested and is also able to send emails to ServerA/domainA. ServerA/domainA is capable of sending everywhere but to serverB/domainB.
All my policies in my router have been reviewed by the manufacturer and they say its A1. My MS Exchange is returning me this error when I try to send to ServerB/domainB:
2014-03-20T17:17:19.149Z,ServerA Exchange SMTP Connector,08D10BB7805F0579,1,,184.xxx.33.242:25,*,,"Failed to connect. Error Code: 10060, Error Message: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 184.xxx.33.242:25"
My ServerA public address has a MX record set at my ISP (domainA.com) so that it can send emails directly but I did not do the for ServerB public address (kind of hard to do because it is a 4G connection (with fixed public IP address and no ports blocked, I am paying more for that).
Finally, if I set my MS Exchange to send through a SmartHost instead (my ISP smtp server), the emails are going through from ServerA to ServerB.
Would anyone know why this is happening?