Different symptoms can occur depending on which disk or partition is running out of space. MTA queues can overflow and reject SMTP connections, messages might remain in the ims_master queue and not be not delivered to the message store, and log files can overflow.
If a message store partition fills up, message access daemons can fail, and message store data can be corrupted. Message store maintenance utilities such as imexpire and reconstruct can repair the damage and reduce disk usage. However, these utilities require additional disk space, and repairing a partition that has filled an entire disk can potentially cause down time.