I am looking for some advice with an Exchange migration. . I have a client that has an Exchange 2007 server but is using Office 365 (no hybrid) and we are migrating them to Exchange 2016. They use Azure AD connect to sync AD to Office 365 but use Exchange 2007 to manage the mail attributes. We are moving them to Exchange 2016 as Exchange 2007 is a out of support. Typically I would upgrade to Exchange 2013 then Exchange 2016 Management tool. They have no mailboxes, all their users have been setup as Mail Users. Do I need to still do the migration or can I decommission Exchange 2007 then install Exchange 2016 management tool and link the AD accounts to Mail Users?
First, let me remind you that you cannot install Ex2016 in an environment which still contains Ex2007 servers, so that sets your upgrade path through Ex2013. I would not start with decomissioning Ex2007, as that in essence means removing all on-prem configuration items related to Exchange, which you then need to re-configure after deploying Ex2016 (e.g. accepted domains). Just follow the regular upgrade procedure for Ex2007->Ex2013, then Ex2013 to Ex2016. Since everybody lives in Office 365 already (assuming you have autodiscover pointing to Office365 and you have no mail relay functionality on-prem, etc), you have no worries regarding namespace, public endpoints etc.