Use upper and lowercase text. Sign your messages with at least your name. Address your messages carefully. Some addresses may belong to a group, even though the address appears to belong to just one person. E-mail messages and news posts are included in the types of works that can be copyrighted.
Criticism is always harsher when written, and e-mail can be easily forwarded.
You may have misunderstood what was meant. Watch out for viruses in attached files. Attached files are a common way to spread computer viruses. In Eudora, just receiving an attachment cannot infect your computer. But opening or running an attachment can.