How can I remove maintenance functions in IMP?

[IMP 3.0]: You need to disable each maintenance function individually. You can do so by editing the file horde/imp/config/prefs.php. You need to locate the stanzas for rename_sentmail_monthly, delete_sentmail_monthly, delete_sentmail_monthly_keep, purge_trash, purge_trash_interval, and purge_trash_keep.

For each stanza, set the 'value' field to 0 (zero) and the 'locked' field to true.

[IMP 3.1]: To disable the maintenance functions by default for all users (but still allow individual users to choose to turn it back on) edit horde/imp/config/prefs.php, locate the stanza for $_prefs['do_maintenance'], and set the 'value' field to 0 (zero).