JSI Tip 1288. If you delete the Microsoft Exchange Service Account.

You can not just create it, as it will have a different SID.

The Microsoft Exchange Service Account is granted specific permissions on the Exchange directory during setup. Thus, when the account is deleted, none of the ACE entries can be resolved. Additionally, none of the Exchange services can start because their account is missing.

Microsoft says that the only solution is to restore the SAM, either from a backup or from the ERD (if you ran RDISK /S).

If you can not restore the SAM, you must reinstall Exchange on all Exchange Servers.

You can preserve information from the Exchange Store (PRIV.EDB and PUB.EDB) but all directory specific information will be lost. You could try to recreate this by using SubInACL.