I am getting an increasing number of corrupt email messages in my inbox. Most problems involve bits and pieces of an HTML message being repeated within the message, but today I noticed that part of one message showed up in another message. The problems show up in plain text and HTML messages. Often it appears to be gibberish with squares and symbols, but often it includes HTML commands.

What could cause such a problem? How can I fix it? I have a large 174 MB pst file.