Regular email client, which can work with any corporate IMAP and SMTP in real time.
As soon as an email is delivered to you, you will see it in your Mail app.
Mail app in OneBox OS allows to understand which contact sent the email just in one click, then quickly get over to this contact's card (Contacts app), filter the whole conversation history with the contact across the company and the structure, and also convert the email into a task or a deal, without having to Copy-Paste the text into CRM-system.
The Mail app collects all emails in background and puts them into the special archive. To review the archive you'd need to install Events app, where all emails, calls and communications are grouped by contacts.