The most common question we receive is "How can we deal with Japanese inquiries through email?" after creating a multilingual website.
This would depend on your application.
Usually, we would recommend our clients to use automatic translation of those inquiries. This is to cut cost on initial correspondent inquiries. Only when details of the business should be discussed, we will assist on translating the emails manually.
Our services could be provided per email basis or through a monthly retainer service.