enumeration

Command	Description
USER username	Identifies the user.
PASS password	Authentication of the user using its password.
STAT	Requests the number of saved emails from the server.
LIST	Requests from the server the number and size of all emails.
RETR id	Requests the server to deliver the requested email by ID.
DELE id	Requests the server to delete the requested email by ID.
CAPA	Requests the server to display the server capabilities.
RSET	Requests the server to reset the transmitted information.
QUIT	Closes the connection with the POP3 server.
Reference	book.hacktricks.xyz - pentesting-imap
Reference	smtp-commands-reference-auth

Connect with service

telnet "$ip" <port>

Telnet POP3 commands:

curl -k 'imap://"$ip" ' --user user:password -v

OR

List all mails

curl -k 'imap://"$ip"/INBOX?ALL' --user user:password -v

openssl s_client -connect "$ip":pop3s