Hi Maciej,
Thank you for yours help.
From your AttachmentTest-output.txt, I am afraid you are using JDK-1.6, because image/gif didn't find the DataContentHandler of image/gif. Between line 14 to 18, we could see the search result for image/gif.
18:10:48,976 FIN | [activation] MailcapCommandMap: createDataContentHandler for image/gif
18:10:48,976 FIN | [activation] search DB #1
18:10:48,976 FIN | [activation] search DB #2
18:10:48,976 FIN | [activation] search fallback DB #1
18:10:48,976 FIN | [activation] search fallback DB #2
If activation could find DataContentHandler, it will look like this, between line 10 to 13:
18:10:48,975 FIN | [activation] MailcapCommandMap: createDataContentHandler for text/plain
18:10:48,975 FIN | [activation] search DB #1
18:10:48,975 FIN | [activation] got content-handler
18:10:48,976 FIN | [activation] class com.sun.mail.handlers.text_plain
Because there are other testcase using javamail.jar, so I can't see the initialization information of mailcap. If you run AttachmentTest separately, you could see how it initialized.
I put my AttachmentTest-output.txt into attach. If you have time, please have a look at it. Thank you very much.