I'm not sure if it's the same issue that I've seen, but we have a similar problem. Manager sends an email to an employee, the employee (Using Seamonkey) replies with the requested information.
Outlook displays it as a blank email. Turns out, viewing the email in the web portal (Show original), will give the email, along with the message that the employee responded with. The HTML codes for color as well. Reviewing the codes, showed to be White background and Black text. Outlook was displaying as white background and very faint yellow text.
The cause is because Outlook uses Word to display HTML code and it doesn't handle it properly. There are no plans by Microsoft to fix it, they suggest, "Use Outlook on both ends"
Ben Franklin quote:
"Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety."