Postal Envelop

In the last year, I have visited our local post office 5 times. Once to collect a parcel of dried mushrooms from a Dongbei friend. Today is the 4th time I went to post a letter oversea.

Collecting a parcel was easy. Just bring an ID (local identity card, or passport) of the recipient and anyone can collect the parcel on behalf.

Sending a letter is also easy. Just show the postal lady the letter and she will inform the postage needed after weighing the letter, except if it is a registered letter. The first time I went to post a letter oversea, I was told the envelop I used was not acceptable, that I had to buy an envelop from another counter, which I did, for just RMB0.10. It was the same size as my envelop, except it was thicker in brown colour. Tore off the envelop from home and rewrite address on new envelop and off it went.

The same happened on my second visit to post another letter oversea, so on my third visit I decided to bring just the letter without envelop, bought the brown envelop upon reaching the post office before fronting the postage lady. On way out, I decided to buy 5 envelops for future use.

Today I thought my letter was perfect when I presented the brown envelop to the postage lady. She said my envelop was not acceptable to send as a registered letter (but thats the envelop you guys wanted me to buy to send my 1st, 2nd, and 3rd registered letters!!!!). She wanted me to buy another envelop from another counter with "AIR MAIL" printed, but the brown envelop was okay to be sent as 'ordinary' letter.
'Ordinary as in Air Mail?' (普通是空邮吗？）
'Yes'.
'Okay, send it as ordinary letter' （那就寄普通信）
'okay. RMB7.00'
'Thank you very much'
'You are welcomed'