query tuning help - Mailing list pgsql-performance

Can any one please help me in tuning the query?

explain
select *
from (select * from crmentity where deleted = 0 and createdtime between (now() - interval '6 month') and now() ) as crmentity
inner join (select * from activity where  activitytype = 'Emails' and date_start between (now() - interval '6 month')  and now()) as activity on crmentity.crmid=activity.activityid
inner join emaildetails on emaildetails.emailid = crmentity.crmid
inner join vantage_email_track on vantage_email_track.mailid=emaildetails.emailid
left join seactivityrel on seactivityrel.activityid = emaildetails.emailid


                                                                                         QUERY PLAN                                                                                        
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Nested Loop Left Join  (cost=8725.27..17121.20 rows=197 width=581)
   ->  Nested Loop  (cost=8725.27..16805.64 rows=7 width=573)
         ->  Hash Join  (cost=8725.27..10643.08 rows=789 width=292)
               Hash Cond: (emaildetails.emailid = public.activity.activityid)
               ->  Seq Scan on emaildetails  (cost=0.00..1686.95 rows=44595 width=186)
               ->  Hash  (cost=8664.41..8664.41 rows=4869 width=106)
                     ->  Hash Join  (cost=5288.61..8664.41 rows=4869 width=106)
                           Hash Cond: (vantage_email_track.mailid = public.activity.activityid)
                           ->  Seq Scan on vantage_email_track  (cost=0.00..1324.52 rows=88852 width=12)
                           ->  Hash  (cost=4879.22..4879.22 rows=15071 width=94)
                                 ->  Bitmap Heap Scan on activity  (cost=392.45..4879.22 rows=15071 width=94)
                                       Recheck Cond: (((activitytype)::text = 'Emails'::text) AND (date_start >= (now() - '6 mons'::interval)) AND (date_start <= now()))
                                       ->  Bitmap Index Scan on activity_activitytype_date_start_idx  (cost=0.00..388.68 rows=15071 width=0)
                                             Index Cond: (((activitytype)::text = 'Emails'::text) AND (date_start >= (now() - '6 mons'::interval)) AND (date_start <= now()))
         ->  Index Scan using crmentity_pkey on crmentity  (cost=0.00..7.80 rows=1 width=281)
               Index Cond: (public.crmentity.crmid = public.activity.activityid)
               Filter: ((public.crmentity.deleted = 0) AND (public.crmentity.createdtime <= now()) AND (public.crmentity.createdtime >= (now() - '6 mons'::interval)))
   ->  Index Scan using seactivityrel_activityid_idx on seactivityrel  (cost=0.00..39.57 rows=441 width=8)
         Index Cond: (seactivityrel.activityid = emaildetails.emailid)
(19 rows)