Email Network Security Blog

What Is an MX Record?

An MX record is a public record in the global DNS (Domain Name System) that specifies which servers handle mail for a given domain name. MX records also specify the priority mail servers should be given in delivery attempts. Consider the following MX records:

yourdomain.com. IN   MX 10 mx1.sentinare.net.
yourdomain.com. IN   MX 20 mx2.sentinare.net.
yourdomain.com. IN   MX 30 mx3.sentinare.net.
yourdomain.com. IN   MX 40 mx4.sentinare.net.
yourdomain.com. IN   MX 50 mx5.sentinare.net.

Here you can see 5 MX records for the domain “yourdomain.com”. They specify how email to the domain “yourdomain.com” should be handled. The first column is the domain name, “yourdomain.com”. The next column is “IN”, which specifies that it is an internet resource (DNS) record. The second column will always be “IN”. The third column specifies which type of DNS resource record it is. In this case, it is “MX”. The third column will always be “MX”. The fourth column is the preference value. It specifies the order that should be used in attempting delivery. We will discuss this in more detail below. The fifth column shows the hostname to which mail should be delivered. This must be an A record. Using a CNAME as a delivery host in an MX record is strongly discouraged.

With the set of MX records above, a given email server attempting delivery to “yourdomain.com” will first try to connect to “mx1.sentinare.net” to deliver the email. If “mx1.sentinare.net” is unreachable or unavailable for some reason (like a network problem or if the server is down), then a mail server should try the one with the next “preference value”, which is “mx2.sentinare.net”. Failing a connection to “mx2.sentinare.net”, the sending server should attempt a connection to “mx3.sentinare.net”. This continues through all the MX records for the domain in order of the preference value. This provides redundancy for SMTP and ensures that a message sent to “yourdomain.com” will be delivered.

Posted in Email Hosting, Email Tips | No Comments »

The Non-Tangible Benefits of Email Filtering

The most tangible benefit to an off-site email filtering proxy service like Sentinare PostGuard is that users stop getting spam and viruses in their inbox– and your users will be very happy about that– but that is only 50% of the true benefit to using filtering service. By using an off-site email filtering service, you can configure your firewall to block inbound SMTP from the world, allowing SMTP traffic ONLY from the servers of the filtering provider. This greatly improves the security of your email server and local area network. Your MX records will be pointing to the filtering service and all your email will come from the servers of the filtering service company.

Be sure to configure your firewall to allow SMTP traffic only from their network. Otherwise you are missing 1/2 of the benefits of the filter. Then, the next time a nasty security bug comes along which requires that you patch your email server, you can do so at your leisure, since your mail server is not available to all the bad guys out there. You will be protected from the 24 by 7 attacks and probes hitting your mail server. If you think about it, there is really no more dangerous protocol than SMTP. Without an email filtering service, your email server is allowing connections from any SMTP client worldwide 24 hours a day. It then accepts data of unknown content from this unknown sender.

A good email filter service provider will also queue your mail when your server is down or the network is unavailable. This makes it even easier when you need to patch your email server. You can safely take down your server and your inbound mail will be held by the mail provider. Sentinare Messaging Solutions holds an unlimited amount of email for an unlimited amount of time.

Posted in Email Security, Network Security | No Comments »

Authenticated Outbound Email (SMTP-AUTH), “Port 25″ and “Port 587″

ISP’s today are blocking port 25 from their users. This is a good thing. Originally mail servers didn’t distinguish between (SMTP) mail traffic from servers and SMTP mail traffic from users. With the rising use of public networks by spammers, a method was developed to segregate server mail traffic from client mail traffic.

First a brief explanation of what a “port” is and how SMTP works. A “port” is a way to identify sending and receiving application end-points on a host. There are “well-known ports” which servers “listen” on. A client knows to connect to these well-known ports to access specific services (like 25 for SMTP and 80 for HTTP). With SMTP, a “client” sends mail by connecting to port 25 on the SMTP server. It connects to port 25, the protocol negotiation happens, and the mail is sent. One more point to make clear is that in SMTP, the “client” is the sending party and the “server” is the receiving party. It is a bit confusing, but an email server, when sending a mail, is an SMTP “client”.

Historically, any party sending email, whether an email server or a user’s email software, used port 25. They would allow anyone inside their network to send mail through their servers’ port 25 to any external address. However, with the rise of spam, this allowed spammers to connect to these networks and use port 25 to spam the world. By shutting down port 25 to IP addresses on the inside of their network, they can block this.

So how do the users send mail now, with port 25 blocked? Enter SMTP-Auth. SMTP-AUTH is a mechanism whereby SMTP is authenticated, typically with a username/password combination. Many email providers, including Sentinare Messaging Solutions, Inc provide SMTP-AUTH on port 587. You can connect through your ISP to mail.sentinare.com on port 587, authenticate, and send your email.

Good email providers, like Sentinare Messaging Solutions, Inc. also allow SSL/TLS encryption to protect both the username/password combination and the content of the email. Good email providers also restrict the sending address to an address “owned” by the user who authenticates. Generally, this is one of the aliases of which the user receives mail on.

Almost every current email client software package supports SMTP-AUTH and can easily be set up. Typically the username/password combination is the same as for inbound email.

Posted in Email Security, Outbound Email | No Comments »

Using Effective and Meaningful Subject Lines in Your Emails

The first two pieces of information a reader sees for each new email item is the sender and the subject. A good subject informs the reader as to the content of the message and helps in managing the inbox.

Here are some thoughts and tips for creating effective subjects:

1. Courtesy: A meaningful subject line clues the recipient in to the purpose of your message before they read it. If they are busy and the subject is non-urgent, this allows them to work more effectively and read your email later when they have time.
2. Concise: Keep it short and to the point. The subject line should be just a headline for the email, cluing the reader into what the content will be. It should not be too short though. (Don’t write a subject line like “info”.)
3. Searching emails: By writing meaningful subjects in your emails, you create search keys for easily finding the message later. Example: If you typically send out a monthly sales report, use a subject like “Acme Corp. Sales Report 200801″. This will allow recipients to later easily retrieve all sales reports from 2008 by searching in their inbox for “Acme Corp. Sales Report 2007″.
4. Mobile Devices: Many people read email on phones and other mobile devices today. In IMAP mode, the clients download the subjects before the bodies. Having a good subject in the email helps them choose which messages they want to download to their phone.
5. Changing The Subject: Sometimes you change the subject in a reply but want to preserve the content from the previous message. In this case, reply to the message and insert a new subject before the old subject. Prefix the old subject with “Was: ” and enclose the old subject in parentheses. Example: Subject: New Design (was: Problem with Existing Design).

Posted in Email Tips | No Comments »

Security Experts List Email Filtering in 7 Security Tips

In an article titled “Seven surefire strategies to block network attacks”, Canadian security experts list email filtering as one of the most important security practices.

There are two benefits to using a provider like Sentinare Messaging Solutions.

1. Blocking spam and viruses: This is the most obvious benefit. Your users immediately will notice the difference in their mailbox when they start getting only the legitimate email they want.
2. Protecting your mail server from attack: This is not as tangible a benefit (unless your email server is hacked). With an off-site filtering service like Sentinare, you can block off public access to your mail server and allow SMTP traffic only from Sentinare’s email servers. This greatly increases the security of your email server and your LAN.

Too many organizations underestimate the amount of work it takes to monitor and protect their email network. Using a spam filtering service will give you not only peace of mind, but it will increase the uptime and availability of your email server.

Posted in Email Security, Network Security | No Comments »

IMAP and the Mobile Device

All the smart phones out there today like the Apple Iphone and Nokia N-series have the ability to access email services. For receiving mail, there are two methods (or protocols): IMAP and POP3. It is important to know that IMAP is the newer and more capable protocol and the one you definitely want to use with your mobile device. I will explain why.

POP3 views the mailbox as a simple mail drop. Your mail client picks up mail from the mailbox, deletes it from the mailbox, and stores the authoritative copy locally on the client machine. With IMAP, your client views the messages on the server and downloads the parts it wants, leaving the master copy on the server. With IMAP, the server copy is authoritative and the local client copy is a “replica”. This has several implications.

With IMAP, multiple clients may simultaneously connect to the same mailbox: Using IMAP, you will see the same set of messages in the same set of folders as on any other computers connected to the same mailbox. This means that you don’t have to sync your phone to your computer. Your inbox is automatically in sync because it is server-based.

Partial MIME message-part fetching: This is probably the most compelling reason to ditch POP3 and start using IMAP on your phone. With POP3, you have no choice but to download an entire message from the list of available messages in your inbox. With IMAP, you can download the body separate from the attachments. This comes in handy when someone sends you a 20MB attachment.

No need to back up the mailbox: If you have a good email provider like Sentinare Messaging Solutions, Inc, then you can be assured that your mailbox is being backed up regularly, with snapshotted backups for the past 15-days. With POP3, the mail that is read by your client is typically deleted from the server, but with IMAP, which is server-based, the messages and folders stay on the server, where they are backed up by your email provider.

Message state information: With IMAP, messages that are marked “read” or “unread” are marked the same way on all IMAP clients viewing the same mailbox. IMAP also supports user-based tags, which are useful for categorizing email.

Online folders: IMAP has support for multiple nested folders stored on-line. POP3 has no concept of folders other than the one inbox.

Server-side searches: IMAP supports running searches on the server. This mechanism avoids requiring clients to download every message in the mailbox in order to perform these searches.

Switch all your clients to IMAP today because it is a big improvement over POP3 and you will be able to take advantage of all these benefits. If you don’t have a decent IMAP provider, go here: Sentinare Messaging Solutions, Inc.

Posted in Email Hosting | No Comments »

Password Security Strategy

Good email security means nothing without a good password security strategy. Too many people have simple passwords and use the same passwords in multiple places. With the rise of identity theft, there is grave danger in using the same easy password for every online login you use. Here is a simple and easy strategy to create and safely save secure passwords.

1. Create a secure password file. It is best to use OpenPGP, or GPG or PGP to encrypt the file.
2. IMPORTANT: Back up the secure password file and the PGP keys on more than one piece of media each stored in geographically separate areas. (Mail a copy and put it in a bank safe deposit box or with a trusted relative).
3. When you create or are assigned a new login,
   • (a) create a secure password. There are many free online web based generators or downloadable programs available by internet-searching for “secure password”.
   • (b) decrypt and edit the password file and add a line. On the line put an identification for the login and then the user id and then the password. Example: travelocity johndoe complexMixeDCASeAndDigitsandspecialcharacters@#R$@#1215
4. Save and re-encrypt the password file.
5. Backup the password file to the media that you have with you frequently and back it up to the remote copy as often as you can.

Now that you’ve created and secured a new and improved email password for yourself, make sure you are using an email provider that encrypts all email protocols with TLS/SSL like Sentinare Messaging Solutions, Inc.

Posted in Email Hosting, Email Tips | No Comments »