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Mail question on Linux Centos

Posted on 2013-11-26
Medium Priority
Last Modified: 2013-11-27
Dear Experts,
I attach port definition from wiki,
Dear Experts,

1-What is major different between SMTP, POP3, IMAP ?

2- What is major different between SMTP, SENDMAIL, PSOTIX ?

3-We always see the word of POP3 is sticked with IMAP, and
STMP is sticked with POSTIX and SENDMAIL, why those are so related ?

4-I know squirrelmail is toll to display email only, but why squirrelmail tools
will know to connect /home/mylogin/mail directory and the email folder ?
I try to copy the email in such directory, for example, support email folder
in /home/myloginmail to new folder such as supportnew but squirrel too
doesn't include supportnew folder. Why ? Whether POP3/IMAP
need to take care all setup for email folder directory so squirrel tools
will get it correctly. How to make sure the tool could also include supportnew
folder. I know I can do it in cpanel, but I had no longer to use it .

Those question reply  is no need as research reports just a brief or idea to let me going into right direction but need a key word to explain it .

Please advise


20 & 21: File Transfer Protocol (FTP)
22: Secure Shell (SSH)
23: Telnet remote login service
25: Simple Mail Transfer Protocol (SMTP)
53: Domain Name System (DNS) service
80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web
110: Post Office Protocol (POP3)
119: Network News Transfer Protocol (NNTP)
143: Internet Message Access Protocol (IMAP)

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Question by:duncanb7
  • 4
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LVL 19

Accepted Solution

xterm earned 2000 total points
ID: 39679825
SMTP is the protocol used to SEND mail.  Mail is sent from a client to a server (sometimes handled by one or more relays) until it is delivered to a destination mailbox by an LDA (local delivery agent, something like maildrop or procmail)

POP3 is a very simple authenticated method of retrieval which allows users to now connect to a mail server and RECEIVE the mail that was already delivered by the SMTP server.  It allows limited functionality such as retrieve and delete, mostly.

IMAP is a more sophisticated authenticated method of retrieval for users.  Rather than POP3 which just allows users to basically get their mail out of a box, the IMAP server is really more for allowing users to manage mail while still on the server.  It supports creating folders for organization, sorting, quotas, and various other niceties.  It's very suited for Webmail applications such as Squirrelmail

SMTP is a protocol, while Postfix and Sendmail are actually SMTP servers (so is Exim).  Each one is a little different, but they three do pretty much the same job.

The reason you see POP3 and IMAP together, is they're both used for reading mail, while SMTP/postfix/sendmail are used for sending mail.  Many users do not know that sending mail, receiving mail, and locally delivering mail are done by 3 different types of software (MTA, POP3/IMAP server, and LDA)

I wasn't really able to understand this question properly, but it sounds like SquirrelMail tools may have been linked in some way to your cPanel installation and it let you have some extended functionality.
LVL 13

Author Comment

ID: 39679836
repeat question 4 only and it is last one if possible,

When I  am in squirrel tools, I can see
the email folder for example, support@mysite.com and then I
go to my directory at /home/mylogin/mail/mysite.com that I can
see support directory and email in /home/mylogin/mail/mysite.com/support/

So I try to copy support directory to new directory like supportnew folder
for testing, and then logout and login again squirrel tools, but I only
see support@mysite.com,   and supportnew@mysite.com is not existed.
I know it is not good test.

The question is I want to ask how squirrel tools will know where it can
find  my support@mysite.com but not supportnew@mysite.com ?
I check all config.php or related file  in  squirrel 's folder that is no
any hint to find out my question answer.

So I believe there must be setup everything done from or by adduser or http.conf to
let squirrel to find out all email folder

 OR email Setup in Cpanel to handle everything for squirrel, if no cpanel, how I can change
to include all email folder directory path besides /home/myogin/mail/mysite.com ?

LVL 19

Assisted Solution

xterm earned 2000 total points
ID: 39679842
Oh, I see, you just made a copy of one of your user's home directories in an effort to create a new user.

You cannot create a user in this way - those folders in /home/mylogin/mail/mysite.com are just user home directories.  The user has to actually exist in the system first in order for Squirrelmail (or any mail software) to find them.

You have to add the user supportnew via cPanel, or whatever you've been using to add users for mysite.com, and then when you log into Squirrelmail, you will log in with the new username and password you created.

It looks like cPanel has it's own passwd and shadow file for each domain in /home/<your login>/etc/<your domain>  You might be able to edit that and add users that way, but be very careful.  Usernames (and other info) are stored in passwd, and the encrypted passwords are in shadow.
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LVL 13

Author Comment

ID: 39679853
Okay, for example,

I created newuser account from adduser and them I make
directory of newuser at /home such as /home/newusers
and then I copy the support directory in /home/mylogin/mail/mysite.com/support
into /home/newusers/mail/newuser.com/supportnew directory

And then logout and login squirrel with newuser login name and its password

after that  I will see supportnew@newuser.com  mail folder on squirrel even I do not have
such newuser.com domain name because supportnew@newusers.com is just
folder only .

But how squirrel will know to go to /home/newuser/mail ? so it must
set up from http.conf, if need http.conf so it needs real newusers.com domain name ?

So confusing,

If what I said that is right, why one domain can have many email address ? I think  I need
supportnew@mysite.com that is possible without need additional or new domain name
of newuser.com  

So it seems there is two question
1- How to have one addition email address at the same domain, mysite.com
2- How to have one new email account at the newuser account and newuser.com
domain name and newuser account password

I need to take a rest and offline, and will continue this after 8 hours, have a nice working day  ,and thanks

Please advise

LVL 19

Assisted Solution

xterm earned 2000 total points
ID: 39679862
Squirrelmail does not use httpd.conf for anything related to retrieving mail, this much I promise you.

When you go to Squirrelmail in a browser it uses the PHP imap() functions in order to make a socket connection to your IMAP server (probably Courier, do "ps ax | grep courier" to confirm if you like.)  Your IMAP server is modified by cPanel to use the passwd/shadow files in the user home directories instead of /etc/passwd and /etc/shadow like the "normal" Courier IMAP server.

So in order to add users with the software that cPanel modified, you need to use their scripts, and of course as I mentioned in your other question, it looks like /usr/local/cpanel/scripts/createuser will do what you need.

As far as newdomain.com, did you already add that via cPanel before it expired?  Because you're not going to be able to add users unless you have the new domain added.  There's probably a different script for that somewhere on the system, kind of like createaccount which is used to add new domains.
LVL 13

Author Comment

ID: 39682082
The question 4 in this thread is deleted since it is not good
way to create email address or folder

LVL 13

Author Closing Comment

ID: 39682087
Thanks for all of your reply

now it is better for solving mail issue

Have a nice working day


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