The Radicati Group’s Email Statistics Report, 2015-2019 says 112.5 billion business emails are sent and received every day, and that vast number is going to increase in the next several years.

The concept of email is simple, but an enterprise mail service is a surprisingly complex beast to run. You might think mail is a prime candidate for shifting to the cloud, making it someone else’s problem. However, even though cloud mail and other off-premise alternatives have been available for many years, pretty much every enterprise still contains a mail network. And they aren’t going anywhere. Here’s why.

The on-premise enterprise mail system

Despite the name, an enterprise mail system doesn’t just transfer mail from outbox to inbox. A mail system has many moving parts, like these.

  • Human-oriented things — clients that talk POP3 and IMAP, and also the time-sucking black hole that is the Personal Information Manager (PIM).
  • Back-office bits — the SMTP network, internet gateway, and other infrastructure.
  • Collaboration features — calendar stores, address book directories, and productivity integration.
  • Security components — filters to deflect the spamming botnets, malware protection, and encryption.

Enterprise mail systems are nothing new — this kind of email setup has been running in every organization for about 30 years. Electronic mail systems (i.e., message store-and-forward systems) are as old as multi-user computing.

The history of the Linux /bin/mail program stretches back to the first UNIX OS in the 1970s. In the dotcom boom of the 1990s, startups used Sendmail on the Solaris OS. Ten years ago, Linux distros were bringing in new mail alternatives like Exim and Postfix. Today all shapes and sizes of mail service are available, and the market is still growing.

On-premise grief

Many software suite suppliers sell mail systems to the enterprise, including IBM, Microsoft, and Oracle. Since these email systems are complex, designing an email service takes expert knowledge. If an email project’s architect is staring into space, she is probably worrying about questions such as these:

  • How do we build DR?
  • What’s the yearly archive growth?
  • PGP encryption or S/MIME?

Life doesn’t get simpler after the transition to operation. Running an email service takes expert knowledge. During operation, a misconfiguration can provide spammers with an open relay, customers with unexpected offers from a Nigerian prince to send them money, and mail admins with a sudden urge to get to know their local RBL (Real-time Blackhole List).

Even if mail admins are totally on the ball, problems can originate down the line. The internet gateway is a constant target for abuse. The ISP insists on plain text traffic. A partner’s poor configuration mysteriously refuses to accept mail.

Isn’t the enterprise mail network a prime candidate for Software as a Service (SaaS)? It’s not difficult to add an external email service. Wouldn’t outsourcing make that pain go away?

You can’t offload the mail system to cloud providers

Email seems like the perfect candidate for offloading to the cloud. In fact,

email was pretty much the first kind of cloudware that the general public experienced. Unfortunately, getting rid of the internal email service is tricky.

While a small organization can make the transition from personal Gmail to Google Apps for Work, a large organization is stuck with one or more legacy email systems. Perhaps the enterprise system was implemented at outrageous cost, or inherited from a company merger.

Legacy mail systems are so embedded in business-critical processes that an operation to remove them is too dangerous to perform. Email is part of the bloodstream of the enterprise.

You can offload some mail to cloud providers

The enterprise can bite off email services a bit at a time. Monitoring systems can be hooked up to the PagerDuty service, so the internal system is no longer responsible for automatic alert mails. Outgoing bulk mail from the marketing department can be handed over to MailChimp. Incoming mail can be run through a cloud filtering service like Comodo Antispam Gateway, Heluna, or Trend Micro Hosted E-mail Security.

The Radicati report shows the average business user sends 34 mails and receives 88 every day. 76 of these incoming mails are legitimate and 12 are spam. Nobody likes a time waster, so removing something that annoys everyone every day is an attractive idea.

You can’t fire the enterprise mail support team

Many organizations are travelling the private cloud route, which does not remove the need for in-house mail expertise. Others have farmed out some mail tools or collaborative components to the cloud.

The enterprise retains some mail services in-house, and probably always will. It’s not because cloud services are too expensive, and it’s not about the money. It’s about how entwined these venerable messaging services are with mission-critical systems and the fabric of the organization.

Note: TechRepublic and Tech Pro Research are CBS Interactive properties.