Post Number
Postal Code, Postcode, Zip Code
noun
You know that a 郵便 is the mail and that a 番号 is a number. So a "mail number," what is that? Usually refers to your post number or postal code. It is also often referred to with a symbol, which is 〒, so look out for that.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
郵便番号は何番ですか？
What is your postal code number?
まだ新しい郵便番号を覚えていません。
I haven’t memorized my new postal code yet.
アメリカの郵便番号は何ケタあるんですか？
How many digits are there in an American zip code?
郵便番号を間違えて書いてしまっていたようで、配達がおくれているみたいです。
Apparently I wrote the wrong post number and the delivery seems to have been delayed.