How will I able to contact or know the e-mail address of a mangaka or the publishers?
Because I have read a lot of unfinished mangas which interests me a lot. And I have already waited for the upcoming volumes for a long time.
So... at least I want to ask them through e-mail.

Sometimes It seems that they don't have plan on publishing the continuations of the unfinished mangas I was referring to. For example, Ueda Rinko's artworks (well I was really referring to her unfinished mangas.) I think almost all of her work arts were unfinished except for those oneshots or mangas that only consists of two to three chapters. For the publisher...If you know the e-mail address of Margaret comics just let me know.
I'm reaallly desperate..hehe.

Your suggestions would be appreciated a lot.

Thank you ^^

No ONGOING-STATUSES please.

Well- if you go to the info page of the manga you're interested in finding out about, you should find the names of the publishers (both Japanese and English, if it was ever licensed) on the lower right-hand corner of the page, below the 'categories' section.
When you click on the link for the publisher, you will go to the info page for that publisher (for example- Asuka, Kodansha, Tokyopop or Viz) from there, you will find a link for their website on the upper right-hand corner of the page. Click that, and you will be directly taken to the website. The website should have info on how to contact the publisher, as well as other information on when the next volumes are due out, and so forth.
I think it's the same for Japanese websites; but of course, you have to know the language if you are going to visit a Japanese web-page. English won't work- and your web-browser has to compatible with kanji and all that.

As for contacting the mangaka directly- I can't say. Some really renowned ones like CLAMP have their own websites (with links on their MU data page), but less-known mangakas' contact info aren't found here. You'll probably have to contact the Japanese publishers for that.

Edit-
I found the Margaret Comics web address; [url]http://margaret.shueisha.co.jp/[/url]
You can usually find these addresses on wikipedia. Or just Google the name of the publisher.
Hope this was some help!

https://www2.shueisha.co.jp/CGI/margaret/message/ouen_mail.cgi

That's Margaret's contact form.

*First empty box ハンドルネーム = Your name/handle
*Buttons 性別 = Gender (女 F / 男M)
*Second empty box 年齢 = Age
*Drop down menu 都道府県名 = Origin ; select 海外 for Overseas
*先生・送り先を選んでください = Who you want to send your message to (Mangaka/editorial)

• マーガレット編集部 (the last option on the drop down menu) is Editorial Department.
• For a specific mangaka, select his/her name from the list. You can refer to the mangaka's page on MangaUpdates for this.

*メッセージ = Enter your message here. Do not provide your detailed address, phone number etc through here. Don't forget to leave your e-mail address, though. ^^

Hope that helps.

**EDIT: remove the space between ma and il in the address.

thanks for all your help..^^

finally I can already send messages and inquire.

No ONGOING-STATUSES please.