We have an existing Kerio Connect with over 1k users. We want to migrate to Exchange 2013, but in a stage phase (groups of users).
Kerio server is configured to manage contoso.com domain and we installed EXCH2013 to manage contoso.com as well.
So the questions are:
Is there a procedure to allow coexistence of two mailserver managing the same contoso.com domain? An example of a desired setup will be to install a third party software (example postfix or sendmail) as a "smarthost". I know how to create rules in sendmail such as "forward mail from/to user@contoso.com to server x". Doing this I can solve the problem of internet incoming mails.
There is a section on Kerio that you can tell if a user is not is its database then forward it to some other host.
However my issue is what happens with emails flowing between kerio and exchange? How can I tell exchange that when a user@contoso.com is not on his database, then forward it to the smarthost or kerio?
Migrating 1k users at once is not an option. Current users in kerio use IMAP with outlook 2007/2010 and Kerio web.
Thanks,