This is a small MySQL script that migrates email addresses and full names from old IMP 2 databases to the identity arrays used in Horde 3/IMP 4. By tweaking the sub-select statement, you can use the same script to migrate existing user data from any external source. Please adapt it to your needs before running it.
INSERT INTO horde_prefs (pref_uid, pref_scope, pref_name, pref_value) SELECT SUBSTRING(user, 1, LOCATE('@', user) - 1), 'horde', 'identities', CONCAT('a:1:{i:0;a:5:{s:2:"id";s:16:"Default Identity";s:8:"fullname";s:', LENGTH(IFNULL(fullname, '')), ':"', IFNULL(fullname, ''), '";s:9:"from_addr";s:', LENGTH(IFNULL(replyto, '')), ':"', IFNULL(replyto, ''), '";s:16:"default_identity";s:1:"0";s:9:"signature";s:', LENGTH(IFNULL(sig, '')), ':"', IFNULL(sig, ''), '";}}') FROM imp_pref WHERE user LIKE '%@localhost' OR user LIKE '%@example.com';
This code takes all entries from the imp_pref table that have the user name ending with @localhost or @example.com. This domain part is then stripped from the user name (SUBSTRING(...)) and a string representing a serialized PHP array is build (CONCAT(...)) from the fullname, replyto, and sig columns and inserted into the horde_prefs table. The IFNULL(...) expressions make sure that this works with both, empty and NULL values in the table fields.
Please note that this script only makes sense for one-time migration of existing data. If you have this kind of user data in an external source permanently, e.g. in a company addressbook, LDAP directory or similar, you should use preference hooks to create the user identities instead.