Data formats
Data formats are the structure of how data is stored.
JSON - is quickly becoming the most popular data format
XML - was the main data format early in the web days and predominantly used by Microsoft systems
CSV - is data formatted by commas. Excel data is typically formatted this way.
What are smtp, pop3 and imap?
SMTP, POP3 and IMAP are TCP/IP protocols used for mail delivery. If you plan to set up an email server such as Mail Server, you must know what they are used for. Each protocol is just a specific set of communication rules between computers.
SMTP
SMTP stands for Simple Mail Transfer Protocol. SMTP is used when email is delivered from an email client, such as Outlook Express, to an email server or when email is delivered from one email server to another. SMTP uses port 25.
POP3
POP3 stands for Post Office Protocol. POP3 allows an email client to download an email from an email server. The POP3 protocol is simple and does not offer many features except for download. Its design assumes that the email client downloads all available email from the server, deletes them from the server and then disconnects. POP3 normally uses port 110.
IMAP
IMAP stands for Internet Message Access Protocol. IMAP shares many similar features with POP3. It, too, is a protocol that an email client can use to download email from an email server. However, IMAP includes many more features than POP3. The IMAP protocol is designed to let users keep their email on the server. IMAP requires more disk space on the server and more CPU resources than POP3, as all emails are stored on the server. IMAP normally uses port 143. Here is more information about IMAP.
Examples
Suppose you use MailServer as your email server to send an email to bill@microsoft.com.
You click Send in your email client, say, Outlook Express.
Outlook Express delivers the email to MailServer using the SMTP protocol.
MailServer delivers the email to Microsoft's mail server, mail.microsoft.com, using SMTP.
Bill's Mozilla Mail client downloads the email from mail.microsoft.com to his laptop using the POP3 protocol (or IMAP).
SMTP
SMTP or Simple Mail Transfer Protocol is mostly used for sending out email from an email client (e.g. Microsoft Outlook, Thunderbird or Apple Mail) to an email server. It's also used for relaying or forwarding mail messages from one mail server to another. The ability to relay messages from one server to another is necessary if the sender and recipient have different email service providers.
SMTP, which is specified in RFC 5321, uses port 25 by default. It may also use port 587 and port 465. The latter, which was introduced as the port of choice for secure SMTP (a.k.a. SMTPS), is supposed to be deprecated. But in reality, it's still being used by several mail service providers.
Now that you have a basic understanding of SMTP, it's time to turn our attention to the two protocols for retrieving email from mail servers: IMAP and POP3. Let's start with POP3.
POP3
As shown in the figure above, the Post Office Protocol or POP is used to retrieve email messages from a mail server to a mail client. The latest version, which is what's widely used, is version 3 - hence the term "POP3".
POP version 3, which is specified in RFC 1939, supports extensions and several authentication mechanisms. Authentication features are necessary to prevent malicious individuals from gaining unauthorized access to users' messages.
IMAP
IMAP, especially the current version (IMAP4), is a more sophisticated protocol. It allows users to group related messages and place them in folders, which can in turn be arranged hierarchically. It's also equipped with message flags that indicate whether a message has been read, deleted, or replied to. It even allows users to carry out searches against the server mailboxes.
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