What does "Cross-forest mailbox moves" enable administrators to do?

"Cross-forest mailbox moves" primarily enables administrators to move mailboxes between different Active Directory forests. This capability is critical in scenarios where organizations merge, reorganize, or need to separate their environments for various operational reasons.

By allowing the transfer of mailboxes across different forests, administrators can ensure that user data and accounts are maintained and migrated smoothly, preserving the integrity of emails and other mailbox settings during the transition. This feature is especially beneficial in environments where multiple Active Directory forests are in use, as it simplifies the process of consolidating or separating mailboxes without requiring complex manual migrations or data exports.

The other options do not pertain to the specific functionality of cross-forest mailbox moves. Managing user permissions, while important, does not inherently involve mailbox movement between forests. Similarly, encrypting email transmissions and establishing transport services relate to securing email communications and routing messages but do not involve the migration of mailboxes between different Active Directory environments.