Accounts support multiple email addresses but do not allow for the same email address to appear on across multiple accounts. Gerrit does support this functionality and it's particularly convenient for contributors that have both WMF and volunteer logins.
Why do you need to maintain separate accounts in phabricator but not separate email addresses?
Quite the opposite, I have separate email addresses and a single phabricator account. I can't seem to figure out what the benefit would be to having a second phabricator account?
I have a WMF email address and volunteer login but I prefer to use my volunteer login whenever possible. It'd be useful to be able to pair the WMF email to my volunteer login but it's already on my WMF login.
I'd like to have Phabricator activity sent to the WMF email account during my employment. If I ever leave the org, I'd like to retain my volunteer account and update my email to point back to my personal email account.
Couldn't you just point a single phabricator account to your wmf email for the duration of your work at the foundation, when that comes to an end, switch phabricator back to your personal email.
I don't know of any policy that would prevent you from keeping your phabricator account after leaving the foundation, though I do assume you would lose your wikimedia.org email, surely it could be arranged to keep your phabricator account in a personal/volunteer capacity.
Thanks, I pointed the WMF account to firstname.lastname@example.org and removing email@example.com. I was then able to add firstname.lastname@example.org to my volunteer account.