I will send my messenger, and he shall prepare the way before me. This passage has multiple applications, as seen in The New Testament usage in reference to the forerunner mission of John the Baptist (see Matthew 11:10; Mark 1:2; JST, Matthew 17:10-14).
It is clear however that Malachi is speaking specifically of the Second Coming, which would mean that one or more messengers (besides John the Baptist) is being referred to in this prophecy.