Is there a way to allow a user who is subscribed to a list with an email address, for example, [log in to unmask] to send postings to the list from this address as well as from [log in to unmask]

It seems to me that I've seen a switch that can be set to let the list be more "
forgiving" of closely related email addresses, but I don't seem to be able to find it...Is there one??...Any help will be greatly appreciated...