TCP/IP creates a connection between sender and receiver using port numbers--the port number identifies a particular application for a particular device; FTP: port 20  SMTP: Port 25  or  HTTP: Port 80

TCP/IP is responsible for providing end-to-end, error-free network connections by transferring (routing) data packets from node to node within the network and making sure that the datagram arrives at its destination exactly as it left the source.

It also determine (TTL) if the datagram is too fragmented and have been hopping around the network for too long and should not be allowed to survive.

See: What is an IP address or email domain address?
 

IP - Internet Protocol, prepares a packet (datagram of 536 bytes (4,288 bits) for transmission across the Internet with the IP header encapsulated. The IP packet is then passed to the next layer where further network information is encapsulated onto it.

Internet Protocol itself is a connectionless protocol, it does not create a session to send data, its responsible only for addressing and routing of packets between computers and does not guarantee delivery or gives acknowledgement of packets sent or lost--which is the responsibility of TCP

TTL
Time To Live
It is a field in the IP header which indicates how long a packet should be allowed to survive before it is discarded. TTL essentially determines the maximum number of hops permitted.

MTA
Message Transfer Agent is the exchange of mail using TCP/IP performed by MTA that defines how email messages are transmitted between two users.

Email Daemon
An email software program residing in a mail server that manages incoming and outgoing mails.