寄信中的平件和特快专递分别用英语怎么说

平信regular 快递 express
当夜的邮寄 overnight
第二天邮寄 second day
三天以上就是 regular

letters delivered ordinaryly 平信.
express 特快专递

Mails a letter even.
mails a letter the special delivery.

standard letter / economic class

express

surface mail
air mail