I need help to make fixed private message table (it expands too far right)

[tercede]

When I view some of my private messages, the table is too far right and does not fit inside the forums outer table width which is at 90% right now. Included in the attachment is the right side of the private message table coming out and making the message board look odd.

Which template do I look at to make that specific table a fixed width and height?