A large message can be stored by separating the message into an envelope portion containing information such as headers, protocols, and addresses, and a payload portion containing items such as file attachments. A means for determining a threshold value provides the threshold value in dependence on the reference value. ; Yg is an optionally substituted C6-14 aryl group, an optionally substituted 5- to 14-membered heterocyclic group, etc. The column which is near the cover is disposed in the axle hole.