The protocol that is being used for sending messages through the router is SMTP.
The SMTP which is a simple mail transfer protocol is a simple electronic mail transmission tool that clients the mail servers and makes the use of agents to send and receive the mail.
Most of the user-level mail clients typically use SMTP only for ending messages to the mail servers for relaying. In the server ports 587 and 465 per RCF.
Find out more information about the email.
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