I am having a very weird scenario in my environment. I have an exchange server 2010 in my premises sitting behind symantec mail security for exchange which again sits behind a firewall named cyberoam (sophos). consider this as domain1.
The second domain (domain2) is hosted with microsoft online exchange (Office365), and has a perfect mail flow as domain1.
Issue: domain1 is unable to receieve emails from domain2 only, where as it is able to send/recieve to all other domains.
domain2 can also send/receive emails from anyone but when an email is sent to domain1, it is not received by domain1.
the weired part is, domain2 receives a successful delivery notification of the mail being delivered. but there is no sign of the email at domain 1
all users of domain1 cannot see or receive any emails from all the users of domain2.
the exchange queue of domain 1 is empty, cyberoam is also not blocking any mails from that domain2, quarantine area is empty and same goes with symantec mail security for exchange.
In short, the mail which is being sent by domain2 to domain1 is lost somewhere even before it reaches the server of domain1.
Troubleshooting everything, but no success, i dont know if anyone else has also gone through the same thing, but are there any suggestions guys?