Post back by registered latter

[Lee12jan]

Hi,

As per continuing a contract, I will pay the member fee by ATM then use a registered latter to post back, below is the dialogue on the phone, please help correct it, thanks

" I will post back by registered latter with the ATM receipt attached"

[Haihao]

I will send back to you a registered letter with the ATM receipt enclosed.

[Lee12jan]

Dear Haihao:

Why not to use 'post' or 'mail' ? Do natives usually use 'send' ?

[Molly]

" I will reply by registered letter with the ATM receipt enclosed/and enclose the ATM receipt/enclosng the ATM receipt.""

[Lee12jan]

Hi, Molly:

Do you know when is 'post' or 'mail' be used in native writing or talk ?

[Molly]

[Lee12jan]

Molly, it seems 'mail' as noun is more common than as verb, right ? e.g. surface mail takes much longer than airmail