My organization is planning to move from Mercury Mail (POP3) to Zimbra Network Edition. Being the lone wolf sys admin in a small company with about 30 employees, I wanted to pitch my thoughts for a migration scenario plays out in my mind to see if my thoughts are correct and if there is anything I am missing, gotcha’s, etc.

The Mercury mail server sits behind a firewall with a private address 10.xx.xx.xx. There is a public IP 200.xx.xx.xx which ties to our email domain externally www.our-companyxyz.com. There is an existing internal dns Alias (CName) mercurymail.ourcompany.com tied to the fqdn for the domain www.our-companyxyz.com, an MX for ourcompany.com tied to the internal 10.xx.xx.xx address with a priority of 10. There is also a static A record tying the internal IP to the hostname of the Mercury mail server.

Mercury being POP3 really is a good thing as far as migration is concerned since there is no data on the server. I guess I am just trying to play out in my mind how to transition as seamlessly as possible. I would like to set the Zimbra server up the same way as Mercury in the sense that the Private/Public setup will be the similar, using the next available addresses in each IP range both internally and externally.

Here is what I am struggling with. I want Zimbra up and fully functional using the same domain name www.our-companyxyz.com (at least internally) before the migration, even if it can only respond by public IP address externally and private IP address internally rather than domain name since it is already in use by Mercury. This is because we need to be able to test mobile phone access and webmail before the migration.

Now of course I want Mercury to be the primary mail server up until the point I flip the switch. Should I simply utilize the same 200.xx.xx.xx external address (existing Mercury mail) as it will still be tied to www.our-companyxyz.com for external use. Is this even an option to consider? And about flipping the switch, will that consist solely of altering the MX record to reflect the new internal address? What am I missing here. Thanks in advance.