Still not possible to do this as I need it.
It looks like bug 78610 had two issues listed in it. The first one was about not seeing errors and was resolved by making DEBUG logging available. The second one was about being flexible with zimbraAutoProvAccountNameMap and was not mentioned again after Comment #7
If I set zimbraAutoProvAccountNameMap to 'mail=%u' it fails with this error in mailbox.log:
If I set zimbraAutoProvAccountNameMap to 'mail' it fails trying to create with this warning in mailbox.log:
com.zimbra.common.service.ServiceException: system failure: AutoProvision: unable to get localpart: null
* It also shows the account it's trying to create as firstname.lastname@example.org@test.local so that's probably why it's failing.
2012-12-27 15:53:21,634 WARN [AutoProvision]  autoprov - unable to auto create account, dn="CN=rightfax test,OU=Users,OU=Test,OU=IT,*REMOVED*"
If I set zimbraAutoProvAccountNameMap to 'sAMAccountName' it creates the email account email@example.com without issue.
If I remove the @test.local from the Active Directory mail attribute then it works too.
Policy requires that I use firstname.lastname@example.org
We have multiple email domains that are not limited to specific OU's as well so need to include the @domain.com part.