These are the services that host the mailboxes. Your account is stored on their servers. To get your email requires connecting to their webmail or using a mail program that supports IMAP or POP3. Examples of email service providers could be your ISP if it gives a free email address with your internet connections, the free service providers such as Gmail / Hotmail / Yahoo, or one of the encrypted service providers such as SCRYPTmail.
E mail clients, does this mean outlook express etc./plug ins.
Email clients are programs on your computer or apps on your phone. Yes, examples of email clients are Mozilla Thunderbird, Windows Live Mail, Outlook Express, or apps such as the Yahoo Mail app or the new Microsoft Outlook app that many seem to think is good.
Encryption / encrypting is the process of converting plain text data into encrypted data. The reverse of this progress is decryption / decrypting. Decrypting is required to view the original data. There are many forms of encryption with a variety of pros and cons including the time needed to encrypt/decrypt and the strength of the encryption; how hard is it to "hack"? Here is a link to an
AES encryption tool that will let you see the process. Example:
Plain text - This is an example sentence in clear text.
Encrypted text:
38 d9 87 a2 a4 3e 4d 9f b4 04 64 c6 2f 49 3d 88
fe 9f de 48 76 49 5f 46 2c b9 07 8e 0a d5 11 00
c9 7f 33 69 0a 92 0c d9 8a 3b 64 48 cd ca 18 7f
If stored on a server or send over the internet, it's easy for anyone along the path to intercept and read plain text, while it's more difficult to intercept and read some types of encryption.
Webmail interfaces are the way to login to an email account using your web browser. Examples are gmail.com and mail.yahoo.com
E mail domain, does this mean that one has to get/pay for a server/host.
The owner of a domain name needs to pay for the domain name to keep it active. If you use a free service such as Gmail then it's Google that pays to keep the DNS for @gmail.com addresses active. It's also possible to register your own domain name such as @lastName..com if no one else has it yet. This is a better option than a free email address for email that you care about since the domain name will be in your control and it can be moved to another email service provider, while a free email account from a service such as Hotmail could be lost if your account is hacked since there is generally limited support for free email addresses.
POP3 (110/tcp & SSL 995/tcp) and IMAP (143/tcp & SSL 993/tcp) are protocols used by email clients access email hosted by an email service provider. Generally, pop3 connections are configured to download email from the service provider to the email client (aka: email program) on your computer, while IMAP is used to access your email (and usually cache a copy on your computer) but leaves the original email messages on the email service providers servers.