While looking at how we were going to define an email address, there were a couple of options.
Many accounts already have a mailbox, so I just want to provide an email address and the other required attributes to those who fall into scope and did not have a mailbox already.
Note that the compulsory attributes required for a basic mailbox are: homeMDB, msExchHomeServerName & mailNickname. By adding the mail attribute, I am defining the primary SMTP address that the person will get. See here for more details: https://technet.microsoft.com/en-us/magazine/ff472471.aspx
Initially, we planned to use and Exchange Email Address policy: https://technet.microsoft.com/en-gb/library/bb125155%28v=exchg.141%29.aspx.
However, there was some fear that if enabled it might have some undesirable effects on those existing mailboxes. So, I went back to code to do the work. The use of Utils.FindMVEntries is not necessarily expensive in this case as the number of people falling into scope at any one time should be low and the likelihood of the first choice not being unique is also relatively low.
Because my organisation is multi-tenant and multi site, there are a number of rules defined to get to the correct suffix and then a valid prefix/ suffix pair.
The MV attribute “provisionExchangeMailbox” is defined in the MV as the person is sync’ed from “HR” via an advanced flow rule. Here is the code: