Microsoft Outlook and Outlook Express allow remote attackers to cause a denial of service by sending email messages with blank fields such as BCC, Reply-To, Return-Path, or From.
Microsoft email clients in Outlook, Exchange, and Windows Messaging automatically respond to Read Receipt and Delivery Receipt tags, which could allow an attacker to flood a mail system with responses by forging a Read Receipt request that is redirected to a large distribution list.
Microsoft Exchange Server 5.5 and 5.0 does not properly handle (1) malformed NNTP data, or (2) malformed SMTP data, which allows remote attackers to cause a denial of service (application error).
Microsoft Exchange 5.5 allows a remote attacker to relay email (i.e. spam) using encapsulated SMTP addresses, even if the anti-relaying features are enabled.
The installation of 1ArcServe Backup and Inoculan AV client modules for Exchange create a log file, exchverify.log, which contains usernames and passwords in plaintext.