A bug in an update to the antispam feature in Trend Micro's eManager meant all e-mail messages containing the letter p were blocked.
Emanager Rule #915 was released last week and contained a flawed routine that blocked and quarantined both incoming and outgoing e-mail containing the letter p, according to Mike Sweeny, a spokesman for Trend Micro.
Emanager periodically installs rules to detect new forms of spam, or unsolicited commercial e-mail.
Trend began hearing from customers about the problem shortly after the rule was released and an updated rule, #916, which fixed the p problem, was released within 90 minutes, Sweeny said.
The flawed rule does not affect any of Trend Micro's antivirus software and eManager is not related to the company's Spam Prevention Service, another gateway antispam technology that Trend Micro released in March and that uses heuristic technology.
Sweeny said that only a small number of Trend Micro customers were affected by the problem, putting the number in the "low double digits".
Because of the severity of the problem, however, Trend notified its eManager customers and resellers of the problem.
The flawed rule has been removed from the Trend Micro Web site and affected customers were advised to install the updated rule, #916 to resolve the problem and receive the updated antispam definitions.
Quarantined e-mail messages could be resent to their intended recipients using features built into eManager, though Trend Micro warned in a knowledge base article that in some cases those resent messages will bypass antivirus screening.
Trend Micro is now reviewing its procedures for producing and testing rules before release and would be tightening those procedures up.
Paul Roberts writes for IDG News Service