Post back by registered latter

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"

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

Dear Haihao:

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

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

Hi, Molly:

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

I’d say that for surface post/mail, “post” is more common in British English and “mail” in American English, but I’m not 100% certain.

For electronic mailing, “mail” is more common than “post” in all major varieties of English.

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