why does outlook sometimes not decode a mime format message?

[Robert Lee]

I receive regular messages from our system server. Quite often, instead of
displaying the email correctly, outlook cannot or will not decode the mime
format. It does not happen all the time. Most of the time I receive the
report correctly and can read all the info, but every now and again it comes
through without decoding and I cannot read the resultant gibberish. I have
not changed any of my settings in outlook.