Mailto: - is an URL (Uniform Resource Locator) that consist of some "Text" followed by the "colon" -- a communication protocol that tells (mail clients or web-browser) program residing in a computer what to do. By using the mailto: command mailto:support @ mailsbroadcast.com it will be translated as a dynamic email address by all mail clients.
 

Soft bounced refers to; mailbox full, mail server down, network busy (ie: 500, 501 Syntax Error) etc.
See: SMTP codes command group

Hard bounced refers to non-existing users (ie: 550, 554, address not allowed or Requested action not taken) Mail servers or email clients that have filtering device can stimulate and return mails as hard bounced.
See: SMTP return codes error
 

MIME - Multimedia Internet Mail Encoding, are the standards for describing email messages being sent over the Internet and specified by: rfc822, rfc2045, rfc2046 and rfc2047 reference available at: www.imc.org/rfc822

IMAP4 - Internet Message Access Protocol Version 4 are used, to hold email messages and allow users to view message heading www.imc.org/rfc2060 or www.imap.org

IMAP4 allows a client mail program to access and manipulate email messages on a remote mail server as if they were local, without the need to download the message or to deliver the message to mail readers and IMAP4 can also relay email message to SMTP mail servers using POP3

Open relay - mail servers that allow anyone (usually forgotten to secure it by IT administrators) to use it to relay emails anywhere (usually hijacked by spammers) for relaying mails to hundred of thousands or millions of recipients.

TCP/IP - Transmission Control Protocol / Internet Protocol creates a connection between sender and receiver using port numbers for a particular device; for example: SMTP Port 25
 

SMTP - Simple Mail Transport Protocol a protocol governing email transmission and reception (sending and receiving emails between mail servers).
 

IP - Internet Protocol prepares a packet (datagram) 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.

Protocol a method of sending and receiving data.

POP3 - Post Office Protocol Version 3 rfc1939 used for delivering messages to (client) mail readers (fetch mails from a remote mail server and store it locally). The email client sends a login (UserID) and a password to authenticate the session. If accepted--the mail client send commands to retrieve messages, then the server transfers the messages and deletes them from the mailbox.

APOP is a POP3 setting that encrypts your username and password, an authentication mechanism designed to protect your POP3 account password when checking mail.
 

MX or Mail Exchangers are database records (registered domains in the "server identity" bank) particulars of domain names of mail server running with SMTP responsible for a domain or a block of domains.

For more information on Email FAQs Glossary see Part -2 Page 2