post
The Italian word 'posta' can be used to mean 'post' in English, in the sense of mail or correspondence. However, it can also mean 'post' as in a position or job, in which case it would be 'posto'. It is important to use the correct form of the word based on the context.
I need to go to the post office.
This sentence is used when the speaker has to perform an activity a the post office, perhaps to mail a letter or a package.
In this context, posta refers to 'posta elettronica', which is the Italian term for email. The sentence is expressing the usefulness of email.
None
The answer is in the mail.
This phrase is used to indicate that a response or answer someone is waiting for has been mailed, and should be received soon.