ADD additional LDAP fields in Zimbra Ver.7 - HOW TO ?

[systemali]

Hello all,
I have a user who is running Zimbra Open Source Server ver.7 and he has a few queries and i am not sure about the answers.
Would appreciate if any one could answer these queries below .
1) The user has 600 users in the domain and most of the mails flow within the domain itself.

He says his mails get delayed a lot and DOES NOT WANT THE MAIL TO GO IN QUEUE, he wants a direct delivery. Is this possible ?
2) Secondly the user wants to ADD 2 additional fields namely ( department & designation ) in the LDAP, so that this will help him run better search query specific to departments.
Would appreciate if any one could let me know if the above is possible in Zimbra Ver.7 and if not what are the alternatives.
Thank you all for your time.