[原文]SMTP server in SLmail 3.1 and earlier allows remote attackers to cause a denial of service via malformed commands whose arguments begin with a "(" (parenthesis) character, such as (1) SEND, (2) VRFY, (3) EXPN, (4) MAIL FROM, (5) RCPT TO.
SLMail contains a flaw that may allow a remote denial of service. The issue is triggered when sending commands containing open parentheses ('('), and will result in loss of availability for the smtp service.
Upgrade to version 3.1 Build 2961 or later, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.