An employee sends an email message to a fellow employee.

Comprehensive and Detailed Explanation From Exact Extract:

SMTP (Simple Mail Transfer Protocol) is the protocol used to send email messages from a client to a mail server or between mail servers. It handles the transmission of outgoing mail. IMAP and POP3 are protocols used for retrieving email, not sending it. SNMP is used for network management.

IMAP and POP3 are for receiving emails.

SNMP is unrelated to email delivery.

This is documented in RFC 5321 and supported by all standard email system operations, including forensic analyses.