The GMm Good Morning mail can be replaced by a GAm Good Afternoon mail, eg. when you were sleeping or doing other things in the morning or... just forgot to write one.
The same for GEm. People just have to be happy receiving a Good mail, even when it arrives in the evening ;)
Usually madelief does write the GMm, sometimes I do, but at this moment it's a long time ago that we've seen one ;(