Eudora 4.x allows remote attackers to bypass the user warning for executable attachments such as .exe, .com, and .bat by using a .lnk file that refers to the attachment, aka "Stealth Attachment."
Qpopper 2.53 and 3.0 does not properly identify the \n string which identifies the end of message text, which allows a remote attacker to cause a denial of service or corrupt mailboxes via a message line that is 1023 characters long and ends in \n.
Microsoft HTML control as used in (1) Internet Explorer 5.0, (2) FrontPage Express, (3) Outlook Express 5, and (4) Eudora, and possibly others, allows remote malicious web site or HTML emails to cause a denial of service (100% CPU consumption) via large HTML form fields such as text inputs in a table cell.
Eudora and Eudora Light before 3.05 allows remote attackers to cause a crash and corrupt the user's mailbox via an e-mail message with certain dates, such as (1) dates before 1970, which cause a Divide By Zero error, or (2) dates that are 100 years after the current date, which causes a segmentation fault.