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Faq says that you need 250 points to be able to vote for migration of questions, but still I don't see how to do that.
migrated from stackoverflow.com May 15 '11 at 18:57
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250 is the minimum reputation you need to vote to close/migrate your own questions. On Stack Overflow you have a reputation of 3000 necessary to vote to close/migrate any question.
If you want to migrate your own question, you click on "close," and then on "off topic."
If the site where you think the question should be migrated is not listed, then you should click on "flag," and then report the reason to flag the question (e.g. "the question better suits XYZ").
If you find a question asked from somebody else that needs to be migrated, then you click on "flag," and then click on "other" and report the reason you are flagging it; this is still the way to report a question needs to be migrated to a site that is not reported in the list you see when you select "off topic." If you click on "it doesn't belong here," you can report a question should be closed, which applies also in the case the question should be migrated.
What I reported is valid for the reputation you have on Stack Overflow. Once your reputation is at least 3000, you can vote to close any question; in that case, you don't need to flag a question to migrate it, except when the site where you think the question should be migrated is not listed under "off topic."
As per recent changes, a question that is 60 days old cannot anymore be migrated, not even from moderators. For those questions, the "off topic" closing reason will show "(too old to migrate)."