Eudora before 6.1.1 allows remote attackers to cause a denial of service (crash) via an e-mail with a long "To:" field, possibly due to a buffer overflow.
https://exchange.xforce.ibmcloud.com/vulnerabilities/16246
http://www.securityfocus.com/bid/10398
http://www.eudora.com/download/eudora/windows/6.1.1/RelNotes.txt