[otrs] 2 queues, 1 of them very slow

Hi list, I have a OTRS 2.3.4 instalacion for a few years. It was working with 1 queue; currently 5,000 tickets after a purge from 50,000. Two months ago a set up a second queue; currently with 200 tickets. I have noted that the fetching mails process takes 4 minutes per message when the target is the first queue, but just a few seconds when the target is the new queue. The mail server I am using is a 2003 exchange to both 2 queues. I did test with qmail but I had the same result. I did set up PostMasterReconnectMessage to 50. I did set up storage to ArticleStorageFS. I did optimize its mysql database. But speed for fetching mail process for the first queue do not improve. :( All help will be appreciated. Thanks