In Brief
E-mail is a very popular form of communication. It involves the transfer of plain text between different computers on the Internet. Electronic mail or e-mail is not suitable for sending confidential data. However, certain encryption techniques, such as OpenPGP, ensure a high degree of confidentiality.
Associated Risks
There are many risks associated with the use of e-mail.
INFRASTRUCTURE
Different software programs cover different roles in transmitting e-mail over the Internet.
MUA - MAIL USER AGENT
The MUA (Mail User Agent) is the software on the computer that allows you to send e-mails. In general, it is an installed software like Outlook or Thunderbird, but it can also be a web application. The MUA forwards an e-mail written to the MTA.
MTA - MAIL TRANSFER AGENT
The MTA (Mail Transfer Agent), sometimes called the SMTP server, takes care of receiving and resending e-mails according to certain rules defined by the administrators of these services. There can be an arbitrary number of MTAs in the path of an e-mail; intermediate MTAs are called ‘relays’ and are becoming rarer these days because traditionally often used for SPAM.
The destination MTA forwards mail to the MDA for delivery to the end-user.
MDA - MAIL DELIVERY AGENT
These are services (often POP3 or IMAP) which receive the mail, store it, and wait for the connection of an MUA for the final transmission of the mail.
How to Protect Yourself?
Depending on the need for confidentiality of your communications (or even classification of data), certain behavioural, organisational and technical advice specific to the handling of e-mails should be followed. Follow the security recommendations for mail servers.