Last week I have installed Exchange 2013 CU1 in coexistence with Exchange 2010 SP3. The installation when well and there were some minor issues with accessing ECP.
For a couple of days everything worked fine and I could send e-mail and when I did a telnet to the host from both internally and external it responded as normal.
But now the Exchange 2013 CU1 machine is not responding anymore. When I migrate a mailbox from the exchange 2010 SP3 server (over a site-to-site VPN connection) or create a new mailbox on the 2013 machine the messages stay in draft and when I try to do a telnet from both internally as externally the telnet command does nothing no message at all it just stays blank.
The Exchange 2010 machine just works fine and those mailboxes can send and receive but I cannot relay messages to the other exchange 2013 machine. I have seen many strange things but this one is weird... I checked the even logs, restarted the machine and services serveral times, changed the DNS in the ECP for both internal and external lookups and even tried to disable the IPv6 in some of the configs but nothing works.
Anyone seen this before?