How long have you had him? If it is less than 3 days, I'd keep him very, very isolated and watch him. Rabbits sometimes react to the stress of a move by sneezing, mucus and sometimes even diarrhea. It shouldn't last long, however. A big clue here is the situation he came from. If his previous rabbitry was clean and the rabbits well taken cared for, I'd lean towards thinking the buck is having a stress-reaction. If the rabbitry was dirty, pans overflowing, overcrowded and the air quality practically unbreathable, I'd probably cull him.
If you decide to watch him for a while, dandilion and dill, fresh or dried, will help boost his immune system and support his respiratory system. If he is not used to fresh or dried herbs, start very small amounts and increase.