UIDs Cannot Start with a Dash

In Messaging Server, UIDs may not begin with a dash character, "-". This is because:



 Messaging Server&#x27;s IMAP implementation uses a user&#x27;s LDAP UID or permanent identifier as their "identifier", and 

 Messaging Server supports the IMAP ACL extension specified in RFC 4314. 



The IMAP ACL extension expresses "negative" rights by prefixing an identifier with a dash character. As such, if Messaging Server allowed as distinct UIDs, the two UIDs "a" and "-a", then it would not be possible to tell if the ACL identifier "-a" meant to allow access to the UID "-a" or to disallow access to the UID "a". This ambiguity can only be removed by either not using UIDs as identifiers or by disallowing UIDs which begin with a dash. Messaging Server chooses to do the latter as the utility of having the identifier be the ACL is quite valuable. Not using the UID as the identifier is counter-intuitive and contrary to the industry norm.

See also:
 * ldap_permid Option
 * ldap_uid MTA Option
 * ldap_uid_invalid_chars MTA Option