A few Hack The Box boxes demonstrate email attacks, such as Rabbit, which deals with brute-forcing Outlook Web Access (OWA) and then sending a document with a malicious macro to phish a user, SneakyMailer which has elements of phishing and enumerating a user's inbox using Netcat and an IMAP client, and Reel which dealt with brute-forcing SMTP users and phishing with a malicious RTF file.
It's worth playing these boxes, or at least watching the Ippsec video or reading a walkthrough to see examples of these attacks in action. This goes for any attack demonstrated in this module (or others). The site ippsec.rocks can be used to search for common terms and will show which HTB boxes these appear in, which will reveal a wealth of targets to practice against.
Easy Lab