Identifies the WorkMail user for the override. Accepts the following types of user identities:
User ID: 12345678-1234-1234-1234-123456789012 or S-1-1-12-1234567890-123456789-123456789-1234
12345678-1234-1234-1234-123456789012
S-1-1-12-1234567890-123456789-123456789-1234
Email address: user@domain.tld
user@domain.tld
User name: user
user