DNS (Domain Name Service) is used to translate human-readable names to IP addresses.
The actual translation is done by DNS servers who communicate with eachother in a hierarchical way.
A name which is registered on the Internet, e.g. mycompany.com.
A name for a computer on the Internet. The last part of the complete hostname is the domain name, e.g. mail.mycompany.com.
A hostname can be translated to an IP address by a DNS server.
IMAP is a protocol that allows mail clients to retrieve mail from a mailbox on a mail server.
IMAP is a bit more advanced than POP3. It allows a mailbox to have several subfolders, and it also allows a mail client to receive a list of the mails without having to download the actial mails themselves.
Every machine connected to a TCP/IP network (like Internet) has a unique number, i.e. an IP address.
Entry in DNS server that specifies which server is responsible for a certain domain.
POP3 is a protocol that allows mail clients to retrieve mail from a mailbox on a mail server.
POP3 is an older protocol with certain limitations. It's better to use IMAP instead.
SMTP (Simple Mail Transfer Protocol) is the protocol mail servers use to communicate with eachother.
Mail clients also use SMTP for sending mails.
This is the network protocol used by the Internet.