설치과정중 자바메일 라이브러리를 설치하지 않으신 것 같습니다.
자세한 내용은 [Download]메뉴에 가셔서 엔메일 리눅스용 메뉴얼을 다운받아보시기 바랍니다.

JDK 가 설치된 디렉토리의 lib 디렉토리아래에 아래 파일의 압축을 풀어넣은후 톰켓을 재시작해보시기 바랍니다.
ex) tar zxvf _jar_webmail.tar.gz -C /usr/local/java/lib/




이재인 님이 쓴 글입니다.
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:※ 필수입력정보 ※
:
:▷ 제품버젼 :
:▷ 사용중인 주소(URL) : http://
:▷ 문제발생시 메뉴/주소 :
:▷ 문제발생시 에러메세지
: :
:
:▷ 질문내용
: :
:
:os: linux (centos 4.3)
:
:
:Nwmail Quick Install Guide 를 참고했습니다.
:
:http://passkorea.net/pubs/nwmail1.1p7.tar.gz
:http://passkorea.net/pubs/_jar_webmail.tar.gz
:
:jdk :1.3.1 18 (http://java.sun.com/j2se/1.3/download.html)
:
:(http://passkorea.net/pubs/j2sdk-1_3_1_01-linux-i386-rpm.tar.gz 는
: glibc버전이 맞지 않아서 사용할 수 없었음. centos는 glibc 2.3 임.)
:
:mysql 4.0.26 (http://downloads.mysql.com/archives/mysql-4.0/MySQL-*4.0.26-0.i386.rpm)
:
:
:
:화면 가득 이런 에러만 보입니다.
:
:Error: 500
:Location: /index.jsp
:Internal Servlet Error:
:
:javax.servlet.ServletException: sun/tools/javac/Main
:    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:508)
:    at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
:    at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:405)
:    at org.apache.tomcat.core.Handler.service(Handler.java:287)
:    at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
:    at org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:812)
:    at org.apache.tomcat.core.ContextManager.service(ContextManager.java:758)
:    at org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:213)
:    at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
:    at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:501)
:    at java.lang.Thread.run(Thread.java:479)
:
:Root cause:
:java.lang.NoClassDefFoundError: sun/tools/javac/Main
:    at org.apache.jasper.compiler.SunJavaCompiler.compile(SunJavaCompiler.java:136)
:    at org.apache.jasper.compiler.Compiler.compile(Compiler.java:273)
:    at org.apache.jasper.servlet.JspServlet.doLoadJSP(JspServlet.java:612)
:    at org.apache.jasper.servlet.JasperLoader12.loadJSP(JasperLoader12.java:146)
:    at org.apache.jasper.servlet.JspServlet.loadJSP(JspServlet.java:542)
:    at org.apache.jasper.servlet.JspServlet$JspServletWrapper.loadIfNecessary(JspServlet.java:258)
:    at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:268)
:    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:429)
:    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:500)
:    at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
:    at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:405)
:    at org.apache.tomcat.core.Handler.service(Handler.java:287)
:    at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)
:    at org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:812)
:    at org.apache.tomcat.core.ContextManager.service(ContextManager.java:758)
:    at org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:213)
:    at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)
:    at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:501)
:    at java.lang.Thread.run(Thread.java:479)
:
: