SMTP is a protocol that handles the delivery of emails between servers. It works behind the scenes to move emails from the sender's computer to the recipient's inbox in a store-and-forward manner, passing through multiple servers along the way and briefly storing emails at each step. An SMTP relay service receives emails from a client and queues them for delivery to the final destination, either successfully delivering the email or returning a non-delivery report. It provides reputation-based filtering to help ensure only legitimate emails are delivered.

1. SMTP
SMTP is part of the application layer of the TCP/IP protocol. Using a process called "store and
forward," SMTP moves your email on and across networks. It works closely with something
called the Mail Transfer Agent (MTA) to send your communication to the right computer and
email inbox.
SMTP spells out and directs how your email moves from your computer's MTA to an MTA on
another computer, and even several computers. Using that "store and forward" feature
mentioned before, the message can move in steps from your computer to its destination. At
each step, Simple Mail Transfer Protocol is doing its job. Lucky for us, this all takes place behind
the scenes, and we don't need to understand or operate SMTP.
SMTP at work.
SMTP provides a set of codes that simplify the communication of email messages between
email servers (the network computer that handles email coming to you and going out). It's a
kind of shorthand that allows a server to break up different parts of a message into categories
the other server can understand. When you send a message out, it's turned into strings of text
that are separated by the code words (or numbers) that identify the purpose of each section.
SMTP provides those codes, and email server software is designed to understand what they
mean. As each message travels towards its destination, it sometimes passes through a number
of computers as well as their individual MTAs. As it does, it's briefly stored before it moves on
to the next computer in the path. Think of it as a letter going through different hands as it
winds its way to the right mailbox.
###remember SMTP sometimes stands for "stop."
Most of us don't know this, but our Internet Service Providers typically have a limit to the
number of emails we can send out over a certain amount of time. Most of the time, it's limited
to a set number per hour or per day.
Each ISP relies on its SMTP to determine (and govern) the email that can be sent out by one
connection. (It is a protocol, after all.) For some people who work at home or manage large
mailing lists, that could be a problem. After they hit their limit, the ISP will simply stop sending
emails. If they think you're a spammer, they might even shut down your account.
What is a POP3?
POP3, which is an abbreviation for Post Office Protocol 3, is the third version of a widespread
method of receiving email. Much like the physical version of a post office clerk, POP3 receives
and holds email for an individual until they pick it up. And, much as the post office does not
make copies of the mail it receives, in previous versions of POP3, when an individual
downloaded email from the server into their email program, there were no more copies of the
email on the server; POP automatically deleted them.

2. POP3 makes it easy for anyone to check their email from any computer in the world, provided
they have configured their email program properly to work with the protocol.
What is a POP3?
POP3, which is an abbreviation for Post Office Protocol 3, is the third version of a widespread
method of receiving email. Much like the physical version of a post office clerk, POP3 receives
and holds email for an individual until they pick it up. And, much as the post office does not
make copies of the mail it receives, in previous versions of POP3, when an individual
downloaded email from the server into their email program, there were no more copies of the
email on the server; POP automatically deleted them.
POP3 makes it easy for anyone to check their email from any computer in the world, provided
they have configured their email program properly to work with the protocol.
Mail Server Functionality
POP3 has become increasingly sophisticated so that some administrators can configure the
protocol to "store" email on the server for a certain period of time, which would allow an
individual to download it as many times as they wished within that given time frame. However,
this method is not practical for the vast majority of email recipients.
While mail servers can use alternate protocol retrieval programs, such as IMAP, POP3 is
extremely common among most mail servers because of its simplicity and high rate of success.
Although the newer version of POP offers more "features," at its basic level, POP3 is preferred
because it does the job with a minimum of errors.
Working With Email Applications
Because POP3 is a basic method of storing and retrieving email, it can work with virtually any
email program, as long as the email program is configured to host the protocol. Many popular
email programs, including Eudora and Microsoft Outlook, are automatically designed to work
with POP3. Each POP3 mail server has a different address, which is usually provided to an
individual by their web hosting company. This address must be entered into the email program
in order for the program to connect effectively with the protocol. Generally, most email
applications use the 110 port to connect to POP3. Those individuals who are configuring their
email program to receive POP3 email will also need to input their username and password in
order to successfully receive email.
IMAP:
The Basics
As its name implies, IMAP allows you to access your email messages wherever you are; much of
the time, it is accessed via the Internet. Basically, email messages are stored on servers.
Whenever you check your inbox, your email client contacts the server to connect you with your
messages. When you read an email message using IMAP, you aren't actually downloading or
storing it on your computer; instead, you are reading it off of the server. As a result, it's possible
to check your email from several different devices without missing a thing.
Mail Servers, Email Clients and IMAP
The easiest way to understand how IMAP works is by thinking of it as an intermediary between
your email client and your email server. Email servers are always used when sending and

3. receiving email messages. With IMAP, though, they remain on the server unless you explicitly
delete them from it. When you sign into an email client like Microsoft Outlook, it contacts the
email server using IMAP. The headers of all of your email messages are then displayed. If you
choose to read a message, it is quickly downloaded so that you can see it - emails are not
downloaded unless you need to open them.
IMAP versus POP
If you think that IMAP and POP are interchangeable, think again. POP works by contacting your
email server and downloading all of your new messages from it. Once they are downloaded,
they disappear from the server. If you decide to check your email from a different device, the
messages that have been downloaded previously will not be available to you. POP works fine
for those who generally only check their email messages from a single device; those who travel
or need to access their email from various devices are much better off with IMAP-based email
service.
Using IMAP
Unlike POP, IMAP allows you to access, organize, read and sort your email messages without
having to download them first. As a result, IMAP is very fast and efficient. The server also keeps
a record of all of the messages that you send, allowing you to access your sent messages from
anywhere. IMAP does not move messages fromthe server to your computer; instead, it
synchronizes the email that's on your computer with the email that's on the server
Main Advantages of IMAP
There are several advantages to using IMAP. First, it allows you to access your email messages
from anywhere, via as many different devices as you want. Second, it only downloads a
message when you click on it. As a result, you do not have to wait for all of your new messages
to download from the server before you can read them. Third, attachments are not
automatically downloaded with IMAP. As a result, you're able to check your messages a lot
more quickly and have greater control over which attachments are opened. Finally, IMAP can
be used offline just like POP - you can basically enjoy the benefits of both protocols in one.
As the world becomes more mobile than ever, IMAP is becoming more and more popular. The
proliferation of smartphones, laptops, tablets and other devices is making the demand for IMAP
stronger than ever. While POP will remain popular with people who only access their email via
one or two devices - and those who have slow connections to the Internet - IMAP is sure to
remain the protocol of choice for most of today's busy people.
8.2 SMTP Relaying Service
"An SMTP relay service guarantees that sent emails arrive in their recipients’ inboxes."
An SMTP relay service is simply an SMTP relay that is run “in the cloud” rather than your own
data center. The service receives a message from your server, queues it up for delivery to its
final destination, and then either succeeds in delivering the message, or generates an “NDR”
(Non-Delivery Report) or “bounce” that is delivered back to the original sender detailing the
reasons for non-delivery.

4. How Our SMTP Relay Service Works
When MailChannels Cloud receives an email message, several steps are followed before the
message is delivered to its intended recipients:
1. The original sender of the email is identified - for instance, if the message came from a
PHP script on your server, identify the script name and path, and the user who is
responsible for it.
2. The email is scanned by top-notch commercial spam and phishing content filters to
identify malicious content.
3. check the sender’s reputation out using our internal reputation system.
4. check whether any of the recipients of the email are actually “spam traps” , which is an
indicator of a severe problem.
5. check the reputation and make-up of the sender’s email domain (i.e. the part after the
“@”) - for example, domains that try to impersonate well known brands like PayPal™
are flagged.
6. If any of the above steps indicate a severe problem, then the email is immediately
rejected. Otherwise, we might take note that the sender is acting suspiciously and be
more vigilant when we see more email from them in future.
7. If everything checks out, then deliver the email to its intended recipients by contacting
the mail servers associated with the email recipients.
8.3 Mail domain administration
it includes
 Changing the mail password
 Deleting an e-mail address
 Forwarding mails
 Forwarding mails without saving copy
 Alias(An alias is an e-mail address with the sole purpose of forwarding mails.
This means that no mails will be saved in a mailbox for an alias e-mail address.)
 Editing an alias
 Deleting an alias
 Catch-all address
 Virus & Spam
 Logging on to webmail
 Setting up mail client

5. 8.4 Basic mail server configuration (send mail, post fix,qmail,exim)