Does the term "E-post" exist (in English)? [closed]

No, in British English email is referred to exclusively as 'email', despite the fact that regular 'mail' is called 'post'. Other nouns associated with email also use 'mail': so 'mailbox', 'mail server' etc. are used.

Post boxes are never referred to as posts. Posts are tall thin things that stick out of the ground. 'Post box' refers to the place where you post a letter to send it. The place where mail is delivered to you is called a 'letter box' (usually).

Canada Post (i.e. the Canadian mail system) has a service called 'ePost' which allows you to receive mail electronically, but the name is specific to that service.