I need some help and suggestion for some mailbox migration. I have an Active Directory domain where all my new Exchange Server 2016 is installed and configured. The domain name is mydomain.com which is also same for public side too (I guess Split-DNS it is called).
Now I have a very old mail server on Windows 2003, using MailEnable 7.5 that is not on any Active Directory domain, using it for the last 4 years. the email domain on the old server is also mydomain.com and for both this old and new Exchange 2016, the mail server is mail.mydomain.com.
Exchange has IMAP, POP, Web based mail and probably MAPI configured too. However the old server is using POP only. (SMTP common on both).
Now I want to migrate all the email from the old one to the new Exchange server. I access old email server using Outlook 2010, so tried using the pst file, the files have a size some 7 to 20 MB in size, but when I import them to the same email user name on Exchange 2016, is says there is nothing on the pst file.
I found it is not possible to do migration, still I am seeking help and suggestion to make the transition possible.
To note: I have tried installing exchange 2007 on another machine to do migration from the old mail enable server to exchange 2007 first, but I cannot install exchange 2007 due to I have already Exchange 2016 installed on my infrastructure which is not allowing the old Exchange 2007 on the Active Directory for integration. Microsoft says it is not possible to install old exchange version once a new one is installed (Exchange is heavily integrated to Active Directory)
I cannot use any paid migration service due to the existing old server is on public side though, the new exchange server is still on private internal network. paid service requires access to both old and new one, and by the way, they are very expensive.
Where I am stuck is, old one is using POP, no option to setup IMAP since I am using the free licenses New exchange is though using all protocol but exchange is very different even using the same protocol specially on authentication, I cannot use outlook pst file from the old server's mailboxes, even cannot install exchange 2007, and also both old and new mailserver is using same domain, just one is exposed to public, and new one is internal. I can expose the new one to public only after completing migration of emails on old server's mailboxes.