Enable Login on Prexisting Alias Domain - How?

[LMStone]

We have a customer with a domain IncrediblyEgregiouslyLongDomainName.com who sometime ago successfully acquired the domain ieldn.com.

At that time, we set up ieldn.com as an alias domain for them, back around ZCS version 5.0.6-ish or so.

Since 5.0.16, it is possible to allow users to login via the alias domain, by enabling zimbraDomainAliasTargetId in LDAP, according to Managing Domains - Zimbra :: Wiki.

That wiki article is not explicit as to how best to set this attribute alone in LDAP, and the related posts here in the forums deal with setting up the alias domain and enabling logins all in one zmprov command.

Since the alias domain is working fine as is (aside from not allowing users to login via the alias), we want to tread carefully here.

Can anyone recommend a specific zmprov command (or sets of commands) to allow users at IncrediblyEgregiouslyLongDomainName.com to log in using ieldn.com?

Thanks!
Mark