One gremlin that causes a large number of E-Mail problems is attachments. Actually the problem is usually not caused by the E-Mail software. Most modern E-Mail utilities handle attached files very well. The problem is usually with the files that are attached. Sometime E-Mail users do not give enough attention to what it is they are sending and receiving. E-Mail just delivers the file, it does not guarantee that the receiver will be able to read it. The same problems would occur even if you mailed a disk my snail-mail.
If you receive one of the dreaded MYSTERY attachments try the following: