Messages .HELD due to some suspicious characteristic will of course exhibit that characteristic. The characteristic could be anything which the site has chosen to characterize as suspicious. MTA Administrators should stay aware of these configuration choices and actions. However, if you are not the only or original administrator of this MTA, then check the MTA configuration for any configured use of the holdlimit channel keyword (12.5.9 Expansion of Multiple Addresses), any use of the $H flag in address-based *_ACCESS mapping tables in the MTA mappings file, or any use of the hold action in any system Sieve file (the system level imta.filter file, or any channel level Sieve filters configured and named via use of sourcefilter or destinationfilter channel keywords; see 12.12.4 Specifying Mailbox Filter File Location); and ask any fellow MTA administrators about any manual command line message holds (through, for instance, an imsimta qm clean command) they might have recently performed. Note also that application of a Sieve filter hold action, whether from a system Sieve filter or from users' personal Sieve filters, may optionally be logged; see the LOG_FILTER global MTA option (Option File Format and Available Options in Sun Java System Messaging Server 6.3 Administration Reference) for more information.