I invited a friend using a referral, but it shows as ineligible.

Tomajev wrote:

She had one older Dropbox account (with different email) and decided to make a new one from my invitation link.

This is almost certainly why - especially if she's had Dropbox on that computer before. 

Referrals are for new users only, not, new users who delete an account and rejoin. 

Tomajev wrote:

What are exact requirements for an email not to be ineligible?

In addition to what Mark stated, the computer you install Dropbox on needs to be one that has never had Dropbox installed on it before, by anyone.

Even if the old account gets "unlinked" from that PC?

The story is short:
She asked me about free cloud-like space to archive some files in the internet and I recommended Dropbox. I've sent her invitation so she would get some additional space. (Because why not. That's what invitations links are for).
The link doesn't work (i.e. creation of new account worked, but she didn't get bonus space) and when she tried to install Dropbox client system told her that Dropbox was already installed.
She created Dropbox account years ago and basically never used it. The account was slowly rotting, forgotten years ago, linked to some old, non-used email address.

Is it possible to unlink the old account from her PC and link the new account so she get the bonus space, or is her PC forever blocked from that utility?

Tomajev wrote:

Even if the old account gets "unlinked" from that PC?

Yes. Once Dropbox has been installed on a computer, that computer can not be used for another referral.

Tomajev wrote:

She created Dropbox account years ago and basically never used it. ... Is it possible to unlink the old account from her PC and link the new account so she get the bonus space, or is her PC forever blocked from that utility?

No, that won't work. That computer will no longer be eligible for a referral because it previously had Dropbox installed. The idea behind referral programs is that they bring in new users that have never used the service before.

Ok, one last question: If she will use a new pc to register, will it work, or is her email address (that received invitation) also cooked forever?
Because it's her email marked at my invitations list as "ineligible".

Btw, that also means that when someone buy a used second-hand notebook (that someone else used for Dropbox), and try to install Dropbox on it, invitation won't work too? What king of logic is that?
Is this verified by MAC address?

Hey Tomajev - sorry to jump in here, but may we reach out via email to have a further look internally with account specific information at this point? 

Also, as Rich mentioned once Dropbox has been installed on a computer, that computer can't be used for another referral (even for an account associated with a different email address).

Sure, you can reach me, I can explain entire situation. (At this point I'm asking rather out of curiosity how that system works, than for that one referral bonus)

Thanks, Tomajev!

I just reached out to you, so we'll continue investigating there.

Hannah, I have the same issue. I recently invited colleagues that have never used Dropbox before, and they showed up as "Ineligible" after signing in from their apps. 

Please award us the extra space, as promised in the share screen!

Hi there, Grizzicle, sorry to see that you're having this issue.

Can you please check this FAQ article, specifically the "Why did I not get my referral reward from Dropbox?" section, to see what might have caused this?

You'll also find possible fixes, so let me know if you're still having this issue after checking everything.