Iftar comes after observing fasting, and we know that non-Muslims do not observe fasting. That is clear. But if conducting Iftar for non-Muslims is meant to strengthen the relation between Muslims and non-Muslims, it is permissible. Allah says, (This day are (all) good things made lawful for you. The food of those who have received the Scripture is lawful for you, and your food is lawful for them.) (Al-Ma'idah 5: 5)
No doubt, such thing can help non-Muslims understand the true Islam and know that Islam is the religion of tolerance, peace, and brotherhood [sic.]. Allah says in the Quran, (Allah forbiddeth you not those who warred not against you on account of religion and drove you not out from your homes, that ye should show them kindness and deal justly with them. Lo! Allah loveth the just dealers. Allah forbiddeth you only those who warred against you on account of religion and have driven you out from your homes and helped to drive you out, that ye make friends of them. Whosoever maketh friends of them (All) such are wrong doers.)(Al-Mumtahinah 60: 8-9)
Besides, Islam was not spread by force; but it was spread by means of intermingling with non-Muslims. Thus, Muslims, in their dealings with others, should appear like the sun that shines and melts away darkness.