A virus is a form of software designed to infect computers, typically with
the goal of spreading automatically to other systems. Viruses may or may not
cause damage, but are frequently associated with some form of undesirable event.
Viruses can be spread via networks (e.g. the Internet or local area network) in
the form of email attachments or downloads, or can be present on a disk or CD.
A Trojan (also called a Trojan horse) is a software program in which harmful
or malicious code is contained within another (seemingly harmless) program. When
this program executes, the Trojan performs a specific set of actions, usually
working toward the goal of allowing itself to persist on the target system.
Trojans can allow hackers to open backdoors on your system, giving them access
to your files and even network connectivity.
An attachment is a file that is attached to an email message. Attachments
are normally considered separately from the body of the email message, and can
be nearly any type of file. Attachments can contain malicious programs, such as
viruses and Trojans, and should be opened with care (and scanned for viruses
prior to being opened).
CC & BCC
CC (Carbon Copy) and BCC (Blind Carbon Copy) fields in your email client
software allow you to send "carbon copies" (or duplicates) of an email message
to other parties aside from the primary recipient. If a user receives a BCC of
an email, the primary recipient will not know about it (thus they are "blind" to
An automatic reply to an inbound email, which typically occurs at the mail
server level. When going on vacation or leave, it's often wise to consider
applying an auto-responder to your email account while you're gone.
An email message that contains angry, and possibly insulting or vulgar,
content. These are typically reactionary based upon some external event.
SMTP / ESMTP
Simple Mail Transport Protocol (and Extended SMTP) are the email transport
protocols that allow email to be sent (outbound) via the network. When you
decide to send an email to another user, your email client communicates with the
mail server via SMTP protocol in order to transmit the message contents.
Post Office Protocol v3 is the transport protocol used for receiving emails.
When you use your email client to retrieve email messages, the client
communicates with the email server via POP3.
MIME (Multi-purpose Internet Mail Extensions) is an extension to the
original suite of Internet protocols (including, but not limited to, email
protocols) that allows users to exchange various types of data files on the
Internet. MIME can be used to transport images, video, programs, and other
binary file formats, as well as the email message text itself.
An MTA, or Mail Transfer Agent, is a piece of software designed to transfer
email from one relay point to another, until the email reaches its destination.
Most mail server software will act as an MTA and pass email messages to other
mail servers in order to facilitate their delivery.
An MUA, or Mail User Agent, is a software program that acts on behalf of the
user. Also known as a mail client, an MUA will allow you to compose an email
message, and send it to the intended recipient.