IMSMO truncates all data, by default, on any message older than 7 days.

There is a USER setting that allows you to set the truncated mail limit on a per user basis - which must be run from the user's machine.

See 'SummaryFilterWindow' here -> https://www.ibm.com/support/knowledgecenter/SSKTMJ_9.0.1/admin_imsmo/adm_set_config_command.html

See this thread -> http://www-10.lotus.com/ldd/ndseforum.nsf/xpTopicThread.xsp?documentId=D572C299ED9E1DEF8525810D005A5836

What Mark Taylor said.

Note that the truncated emails open fully and include all data if you either double-click and open them in their own window or click on the "View Full Message" button in the IBM Mail add on in the Outlook toolbar.  They simply don't show fully in the preview pane when older than 7 days.

I sincerely hope in the near future that IBM adds optional functionality to have truncated emails retrieve automatically in the preview pane when clicked on.  It would be a workable compromise between the server workload (thus the "truncated" email body) and user expectation.  Outlook would then feel 95% normal and function almost transparently compared to working against an Exchange server.