On first day of Microsoft Ignite 2017, Microsoft announced the broad release of Exchange 2019 in H2 of 2018. The TAP program is open for application. This definitely answers some questions for us, like “Will Exchange Server 2016 be the last on-premises version?” Microsoft has little interest in ending Exchange on-premises for the foreseeable future; they are the only [viable] vendor that has an on-premises and a cloud offering that can work well in a hybrid configuration (sure, IBM has this with Notes, but I don’t see new customers adopting Notes whereas I see plenty of organizations moving off of Notes). So, they have a strategic advantage.
However, this does have some very serious implications for Exchange customers that have not yet moved off of Exchange 2003 (they still exist… I heard about a decent sized environment yesterday). With the release of Exchange 2019 and the standard support cycle, we will see the EOL of Exchange Server 2010. Exchange Server 2010 was the first version of Exchange to support hybrid configuration with Exchange Online. In addition, it is the newest version of Exchange Server that can co-exist with Exchange 2003. When it is EOL, there will be no support for it in hybrid configuration (though, it might work, for a time). So, if you have an Exchange 2003 environment and you intend to move to Exchange Online, you will not have a supported direct path that includes rich hybrid co-existence.
This won’t be horrible for smaller organizations that could get by with a cutover migration. Where it will sting is organizations with 500+ mailboxes. So, there are a few options for organizations on Exchange 2003 right now:
1) Migrate to Exchange Online before Exchange Server 2010 is EOL;
2) Migrate to Exchange Server 2010 on-premises and be prepared for hybrid co-existence at that point with Exchange 2013, or newer; or
3) Make moves to get up to a modern version of Exchange sooner rather than later.
If your organization is still on Exchange 2003, you don’t have a good record of staying up to date, so I wouldn’t make an ambitious plan to do a double-hop migration to Exchange 2016 and think that you will remain in the realm of current unless you are ready to invest significantly in this. The other thing to keep in mind is supported versions of Outlook. Today, Outlook 2010 will work with Exchange 2003 and Exchange Online. When Office 2019 is released, Office 2010 will also be set for EOL. This will complicate things even further.
It’s time to finally make the move off of Exchange 2003 if you’re still using it.
Dustin Dortch 
Alternatively, the customer can also just stay with office 2003 and exchange 2003. The only REAL need to constantly move to a new version of anything is the one of two things – it solves a business problem, OR it creates/maintains cash flow for the vendor.
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or it solves security flaws that are no longer patched.
I’m doing an Exchange 2003 to 2019 upgrade soon. Think I’ll just Exmerge out mailbox data to PST files, uninstall Exchange 2003 completely, upgrade the domain then install Exchange and restore PST back to mailboxes. Cleanest way at least, easier than double hop upgrade.
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If it is a small organization, perhaps. However, doing upgrades… it would be a triple hop, Exchange 2003 > 2010 > 2016 > 2019.
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