Non Existent User Login Attempts

Log contains several messages from dovecot that are not clear to me exactly what is occurring, single example below. These appear to be login attempts for the same group of non existent user ids from various rip addresses. Am I interpreting these correctly and, if so, is there any issue with just ignoring them?

dovecot: pop3-login: Disconnected: Connection closed (auth failed, 1 attempts in 0 secs): user=<non-existent-user@example.net>, rip=0.0.0.0

Thank you, Bryan