Finding email and message using yahoo?

I made a friend with a Japanese exchange student but didn't have enough time to talk so I quickly asked for her email which uses @docomo.ne.jp
I tried using my yahoo account to see if she would respond but doubt it would work and would probably automatically rejected because it's a foreign email. I'd like to find her and continue to talk more. I want to know if there's any way that I could communicate to her.

Have you tried it from your yahoo account? Just try it - some people accept only registered e-mail addresses (but then there is no point in giving out that address), and some people for security might block non-mobile addresses, but others simply do accept messages from new address, either mobile or whatsoever. You will have to try it. Best wishes.

Her email with the @docomo.ne.jp domain should work just like any other email address, if you are not able to get a hold of her with your yahoo email, you could always try sending her messages from other email addresses you might own?

historically, many spam mails have been sent in Japan from yahoo and other free mail systems. thus, I think the initial setting is "not accepted".
generally speaking, if you use a free mail address, it means you don't want to show up yourself to the receiver.