proguard failed when using javamail API to send email

proguard failed when using javamail API to send email

I am using the javamail API to send email and httpclient for network
access in my app. I refer to the demo gmailsender.Here is the Link:
Sending Email in Android using JavaMail API without using the
default/built-in app
There is no error when debugging and I can run APK smoothly in my
phone.But,when I tried to use proguard generate my signed APK ,I found the
console showed me "Proguard returned with error code 1", although I do as
the solution Android, javamail and proguard. As a result, I can not built
my APK with Proguard.
Can anyone give me a help? The console showed as following:
Proguard returned with error code 1. See console
[2013-09-06 10:32:25 - ] Note: there were 1487 duplicate class definitions.
[2013-09-06 10:32:25 - ] Warning: library class
org.apache.log4j.net.SMTPAppender$1 extends or implements program
class javax.mail.Authenticator
[2013-09-06 10:32:25 - ] Warning: there were 1 instances of library
classes depending on program classes.
[2013-09-06 10:32:25 - ] You must avoid such dependencies, since
the program classes will
[2013-09-06 10:32:25 - ] be processed, while the library classes
will remain unchanged.
[2013-09-06 10:32:25 - ]
(http://proguard.sourceforge.net/manual/troubleshooting.html#dependency)
[2013-09-06 10:32:25 - ] java.io.IOException: Please correct the above
warnings first.
[2013-09-06 10:32:25 - ] at
proguard.Initializer.execute(Initializer.java:369)
[2013-09-06 10:32:25 - ] at
proguard.ProGuard.initialize(ProGuard.java:212)
[2013-09-06 10:32:25 - ] at proguard.ProGuard.execute(ProGuard.java:87)
[2013-09-06 10:32:25 - ] at proguard.ProGuard.main(ProGuard.java:484)