Description:
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поддержка@почта.рус is a real email address, but FILTER_VALIDATE_EMAIL fails to validate it, regardless of FILTER_FLAG_EMAIL_UNICODE

Test script:
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<?php
var_dump(filter_var('поддержка@почта.рус', FILTER_VALIDATE_EMAIL, FILTER_FLAG_EMAIL_UNICODE));

Expected result:
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bool(true)

Actual result:
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bool(false)