There is always going to be some interaction between Iran and Persian-speaking (Tajik Northern Alliance)Afghans. Iran certainly does not want its investment in the Northern Alliance to go to waste.
However several years ago the Taliban massacred about a dozen Iranian diplomats at a consulate in Afghanistan and the Iranians almost went to war against them. It doesn't seem real likely the Iranian government is consciously and deliberately welcoming these same people.
The Taliban massacred Iranians. Why does that preclude them from harboring Al Qaeda who are mostly not Afghanis?