A: A receiving line isn't old fashioned, nor is it required. The only requirement: that the bride, groom, and hosts speak with all of their guests. For large weddings (75 people or more), a receiving line—either just after the ceremony or as guests enter the reception—offers the most efficient way to do this. At smaller events, where there's ample opportunity to greet guests casually, you can more easily achieve this. Some couples achieve this by visiting each table during dinner, though it does cut into your own to enjoy the meal!
The receiving line usually includes (in order) the bride's parents (mother first), the groom's parents, the bride and groom, the maid or matron of honor, and the bride's attendants. If the wedding party is small, the best man and may join as well, though flower girls and ring bearers are not included. If either the bride or groom has stepparents, they stand with their new spouse. If the divorced parents are unable to be that close to each other, it's okay to arrange the line to allow for a little breathing room between them or to excuse someone altogether if they don't feel able to participate. —Anna Post, The Emily Post Institute