Blackberry - Daily Password Validation Issue

Before this issue resolve, my user received daily message in their BB to validate their work email password. I need to validate their email password at their BIS account daily. Actually it is very annoying. At last my issue resolved by doing the following:-

-Try reducing the number of email messages in the mailbox to below 900 or 1000. Start with moving the largest email messages to a sub folder or deleting them-