Where to find the member "uid" ?

The member "uid" has "Unique Identifier" is used on all services to find the correct user in the LDAP database.

Difference between single domain and multi-domains:

If you have enabled the multidomain ( see multi-domains on Cyrus-imap or multi-domains on Zarafa ) the uid must be on the user@domain.tld form. if not then the uid will be a single word.