Generally SMTP.
the protocol used for email is simple mail transfer protocol and the layer is transport layer.
Simple Mail Transfer Protocol, is the technology used to send out email messages. It goes hand in hand with POP (Post Office Protocol) that is, typically, employed for receiving emails from a web server to an email program or an email client.
Pop3
IMAP4
SMTP (Simple Mail Transfer Protocol)
SMTP (simple transfer mail protocol) which is used as the outgoing mail server and it uses port number :25 POP3 (Post Office Protocol 3) is the most recent version of a standard protocol for receiving e-mail. POP3 is a client/server protocol in which e-mail is received and held for you by your Internet server and it uses port 110
Port 25 (Simple Mail Transfer Protocol)
I assume by 'outgoing letter' you mean an email? If so, then a copy of the email can be found in the Sent folder, found below Inbox.
wich of the followting protocol is used to receive email?
POP (Post Office Protocol) - The protocol that an e-mail server and client usewhen the client requests the downloading of e-mailmessages.
SMTP
SMTP (Simple Mail Transfer Protocol) - sends mail only POP (Post Office Protocol) - retrieves mail and manages mailboxes IMAP (Internet Message Access Protocol) - retrieves mail and manages mailboxes