Mail Protocols – IMAP and POP

Most of the core Internet users should have heard of the E-mail Protocols – POP3 and IMAP. In this post, I’ll explain the concepts.

IMAP

Internet Message Access Protocol (IMAP) is an Application Layer Internet Protocol. It listens to Port 143. IMAP allows a user to access E-mail which is stored on a Remote Server. IMAP is used to retrieve messages from a Mail server. In IMAP mode, Multiple E-mail clients can interact to the same account on the server, from anywhere. Also, E-mail clients can talk to multiple servers. Its upto the E-mail client who decides about the storage of messages – either locally or leave them on the server.

IMAP is currently the most desired Mail protocol used since it has many advantages over POP3. They are :

1) Continuous mode of Connection : Using IMAP a client can interact with the Mail server throughout, whereas using POP, this would be impossible. POP connects to the server for the retrieval of new messages. With an IMAP connection, as long as the User interface is active, it connects to the server and download content.

2) Multiple mailboxes : IMAP clients can create, remove, rename mailboxes in the server and allowed to move messages between the folders.

3) Simultaneous Connection : POP allows only one client (currently connected one) to the mail server, whereas IMAP allows multiple clients simultaneously connected to the server and manage it. Changes made by the clients will be updated concurrently.

IMAP Telnet Commands

In this section, I would like to explain how an E-mail account can be managed through Telnet. The real domain name and IP has been masked

Before we go, there is one more thing to explain. Since IMAP allows multiple connections, we need to type a command tag before we enter the actual command. This could be anything – like a period (.) or numbers or alphabets. The server will respond with the command tag we entered, indicating the connection we use. For example – I have used a period (.)  and the server will respond with the . tag along with the output of commands. If another user inputs the command tag as 1 or a then the server will bind its response with the command tag 1 or a.

a list "" "*"
* LIST (\HasNoChildren) "." "INBOX.Trash"
* LIST (\HasNoChildren) "." "INBOX.test44"
* LIST (\HasNoChildren) "." "INBOX.Junk"
* LIST (\Unmarked \HasChildren) "." "INBOX"
* LIST (\HasNoChildren) "." "INBOX.Sent"
* LIST (\HasNoChildren) "." "INBOX.Drafts"
* LIST (\HasNoChildren) "." "INBOX.test_imap"
a OK LIST completed

Note that the command tag ‘a’ is added to the response returned by the server, in the rest of the blog, I’ll be using . (Read the rest of this entry…)

Prevent your mail/IP from getting marked as SPAM/Blacklisted, A few TIPS!

“SPAM“! A word familiar to all Netizens.

Emails plays a major role in today’s business, one must be keen to preserve the authenticity of mails they sent to the users and fail to do so may result in getting your mail server IP blacklisted and mails ends-up in users junk folder and they die!

This post is not a perfect guide to prevent you from getting blacklisted by the spamcops, but a few tips that could save your “Time” and “Reputation”.

1) All email is filtered against published blacklists of spam servers. Check whether your mailserver IP is already blacklisted : http://www.mxtoolbox.com/. If listed, take necessary actions to remove it. You can temporarily switch the mail server IP to get the mails moving until your regular IP is released.

2) All mails will be filtered based on certain rules. It looks for senders email address, mail subject line and words on the message content. Avoid using blank subject line and using common spammers words like “offer, discount, sale, free etc… There are a lot more..

3) Maintain a regular time intervals while sending mails to a particular sender. This could be setup on exim configuration file. (Needs admin privileges)

4) Enable SPF:
Sender Policy Framework (SPF), is an e-mail validation system designed to prevent e-mail spam by addressing a common vulnerability, source address spoofing. SPF allows administrators to specify which hosts are allowed to send e-mail from a given domain by creating a specific DNS SPF record in the public DNS for that domain. Mail exchangers then use the DNS to check that mail from a given domain is being sent by a host sanctioned by that domain’s administrators.

If SPF record is enabled for a domain, spammers and phishers are less likely to forge e-mails pretending to be from that domain. Spam filters now check for SPF records and hence eliminate the chance of forged mails, spams. Hence an SPF protected domain is less attractive to spammers and phishers and is less likely to be blacklisted by spam filters and ligitimate mails will go through.

SPF keeps the detail of the machine which is only authorized to send mails for that particular domain. This is done by adding additional a TXT record to their existing DNS records. Mail receivers that checks for SPF records check the domain DNS and finds whether the server is allowed to send mails for that domain.

(Read the rest of this entry…)