What is EFS?
EFS is a "POP3 Connector" (also known as "mail forwarding" or "mail relay" software etc). It was originally designed to provide a cost-effective way of retrieving Internet based mail from a Pop3 account and delivering any messages to an internal mail server, such as Microsoft Exchange Server, Lotus Notes/Domino (or in fact any RFC compliant SMTP mail server). You do not need a fulltime connection to the Internet to run EFS - it works with both static (full time) and dynamic (part time) IP addresses.
The best part about EFS is that once its setup, it is basically maintenance free. Similar mail retrieval programs usually require you to add a separate mailbox for every user that mail will be distributed for - the simple downside of this, continuous maintenance and double data-entry. EFS does away with this by allowing you to specify the domain that you will be accepting mail for (just as you are required to do for your mail server)
NOTE THAT EFS IS A ONE-WAY OPERATION (ISP MAIL -> EFS -> LOCAL MAIL SERVER) IT DOES NOT SEND MAIL FROM YOUR MAIL SERVER TO THE INTERNET. Typically this is done automatically by simply configuring an "SMTP SMART HOST" or by using "DNS LOOKUP" available on most Mail Servers
How does it work?
Consider the following scenario...
- You have an Internet Service Provider (ISP) account, eg: "chimera"
- You have a domain name "chimera.co.nz" and your ISP has the "catch all" feature setup (available from most ISP's). This simply means that any mail sent to email@example.com (where xyz = anything) will go to your single ISP account
- You are running a local Mail Server (eg: Microsoft Exchange) which is setup to accept mail for your domain "chimera.co.nz"
- You have an Internet connection
- LAN users can send email to one another internally and external email is sent out by your mail server
- You need a way to get external mail (mail in your ISP "chimera" account) into users mailboxes.
How EFS plays it's role...
- You would setup EFS to accept mail for your domain, eg: "chimera.co.nz"
- It checks for mail from ISP "chimera" POP3 account at your ISP
- It then works out and addresses to the intended local recipient(s) sending those message(s) to the local mail server.
- The mail server distributes the messages into the appropriate users mailboxes, or, if the user doesn't exist, returns an NDR (undeliverable) message back to the original sender.
Since EFS "extracts" and addresses the messages to recipients for your domain only, in this case "chimera.co.nz", the mail server will accept the mail and deliver it to the appropriate person(s).... but I hear you ask yourself...
But why do I need EFS to accept mail specifically for my domain?!
To demonstrate, let's take the following example. Say a message was sent:
Subject: Test Message
The initial mail server accepting the message (ie: Alien's SMTP server)
will deliver the message, effectively, to the "chimera" and "flintstone" mail accounts. However, when the message is read from the "chimera" mail account, it will still have both these recipients in the "To:" address. If EFS was to forward the whole message, then Fred would receive "Test Message" twice as your own mail server would also send it to him! When EFS get's the message, it addresses and delivers only to those recipients intended for final delivery, in this example, <firstname.lastname@example.org> (however, the mail client will still be able to see that the message was delivered to both Fred and James)
This is why you must enter a domain to accept mail for in EFS (the same as you would do for your Mail Server)
But what if I already have a direct SMTP feed into my business?
If you have a full time Internet connection, a static IP address and a primary MX record used to send mail directly into your business, you should still consider a secondary MX record for redundancy. The benefit of using a Pop3 connector for secondary mail is that its far less likely that your Internet Providers entire infrastructure will go down than your own Internet connection. The majority of Mail servers have staggered retry periods for failed mail delivery. In other words, mail delivery will be attempted on a periodic basis until delivery is successful, however these times can increase considerably with every failed attempt (often up to 12 hours or more). The alternate option is to have a secondary MX record setup that points to a catch-all account at your Internet Provider to accept that mail while your Internet connection was down. When your Internet connection comes back up, EFS will check that account and deliver mail to your staff almost immediately. If your business has SLA's around mail delivery times, you could install a cheap secondary Internet connection that could be brought online and used by EFS to collect mail.