Concept:Email servers use a dedicated protocol to send and relay messages between one another over the internet.Explanation:SMTP, which stands for Simple Mail Transfer Protocol, is the standard protocol used for transmitting electronic mail between servers.It handles the sending and forwarding of email messages from the sender's server to the recipient's server.The other protocols do not serve this purpose: SNMP manages network devices, FTP transfers files, and POP is used to retrieve email from a server to a client.Therefore, the protocol used between Email servers is SMTP.Answer:A. SMTP