Hi, just in case you haven't solve the issue yet.
UPDATE. This is from a tech magazine, and it was highlighted by Mrko5 on Microsoft community.
Outlook 2003 messages are cut off
Following recent Windows updates, Outlook 2003 users are complaining that replies are cut off, chopped, or truncated, with only the draft version being sent. Some users say only the initial draft copy is saved, not additional drafts after editing a message
for a period of time.
Every so often, not all the time (which is what has me baffled), an email will be composed and sent by the user, however, all but the first couple of lines are cropped off. In some cases, the email is just sent with the first line. This problem is random,
and does not affect all emails.
This problem affects only people who are using the Outlook Editor, and only if you take longer to compose and send a message than the "AutoSave unsent every" setting is set for (default is 3 minutes).
Outlook is sending the message from the draft folder and it's often not the final copy. Messages that are composed and sent quickly will be complete, messages the user takes longer to write may be incomplete. Replies to plain text messages aren't affected,
but replies to HTML messages might be cut off, if the user sent it before the draft was created.
If using Word as the email editor is not an option, you can use Plain Text message format. Either of these changes are made in the Tools, Options, Mail Format dialog box. You don't need to use Word as the editor AND plain text, one or the other is enough
to fix the problem.
If you want to use the Outlook Editor and HTML (or RTF) message format, press Ctrl+S or the Save button to re-save the draft before sending the message to update the draft copy and the complete message is usually sent. However, some users reported only
the first draft is ever sent.
You can also change the default time before autosave kicks in. The default is 3 minutes. If you complete most messages quickly increasing the time will help, or you can lower it to 1 minute, especially if you tend to pause before sending a message. Make
this change in Tools, Options, Email Options, Advanced Email Options.
If none of workarounds above are acceptable, you can uninstall Internet Explorer 11 to eliminate the problem. You'll need to configure Windows Update so that IE11 does not get reinstalled, otherwise, the problem will return with the next Windows Update.
To prevent IE11 from being reinstalled, you'll need to Hide it the next time Windows Updates offers it. Select it from the list of Updates waiting to be installed, right click and choose Hide update.
Administrators can run the blocker in the IE11 toolkit from Microsoft at Toolkit to Disable Automatic Delivery of Internet Explorer 11, then restart Windows.
Hope it helps.