Variable mailboxSetValidationPluginConst

Validates server-defined constraints for Mailbox/set operations.

This plugin enforces account-specific mailbox creation limits defined in the Email capability:

Mailbox Name Length (RFC 8621 Section 2.2):

• Validates that mailbox names do not exceed maxSizeMailboxName octets (UTF-8 encoded)
• The limit is server-defined and specified in the account's Email capability object
• Prevents creation attempts that would be rejected by the server

Top-Level Mailbox Creation (RFC 8621 Section 2.2):

• Checks the mayCreateTopLevelMailbox server capability
• Prevents attempts to create mailboxes with parentId: null when the server prohibits it
• This restriction varies by server implementation and account type

These validations catch client errors before sending requests to the server, providing immediate feedback and avoiding unnecessary network round-trips.