In the early 2000s, many security professionals advised disabling your email client's preview function. Simply previewing an email could be dangerous! This is no longer good advice. With a modern email client, you can preview all the emails you want.
Unless You Have a Time Machine, It's Safe
We recently posted an article about how to turn on the preview pane in Gmail. Through article comments, emails, and Twitter DMs, we got quite a few people asking us if it was safe to use the preview pane.
Back in the day, articles advising disabling your preview pane were commonplace. Many websites made the case that using the preview pane option was a Bad Idea. They often didn't specify why, other than saying you "may open an email message that you really didn't want to open." The implication is that a virus or other nasty thing might get on to your computer if you open an infected email. To be fair, this was a problem for a short while back in the early part of the millennium.
Once email started using HTML for formatting, some malicious actors took advantage of this to execute code--- usually JavaScript---when an email was read. For a short period, it was considered dangerous to open mails, and by extension use the preview pane, unless you were sure the email was safe.
But the major email developers of the time, including Microsoft, Pegasus, Eudora, and Apple (there was no Gmail at this point), got on the case very quickly. Within a few short years, the problem was virtually gone because all of the mail clients stopped allowing code to be executed when an email was open. No mail client now allows code to be executed when you open an email, and they haven't allowed this for well over a decade. So, unless you're using a very, very old, unpatched email client (think Outlook Express circa 2000 on a Windows 98 machine) your mail program simply won't allow code to execute when you open an email.
Unless you're reading this article from the early 2000s with a time machine, you should be safe.
Here's the Real Danger
On top of this, all the major providers of email accounts, including Microsoft, Apple, Gmail, and Yahoo! have sophisticated virus and malware detection tools that stop viruses and malware getting to your inbox anyway. This doesn't mean that there is no threat from email, but the threat now requires you to do something like open an attachment or click a link. Worryingly, there are occasional articles that still suggest the preview pane is a danger, but we wouldn't recommend following such outdated and incorrect advice.
The problem doesn't exist anymore, so by turning off the preview pane, the only thing you're doing is making life more difficult for yourself.
As we've put it before, opening emails is safe. The risk comes from following phishing links and opening dangerous attachments. Those risks are the same whether you're using a desktop client like Microsoft Outlook or web-based email like Gmail.
Unless your email client or web browser contains an unpatched security hole malicious emails can exploit, you're fine. That shouldn't be the case---you should be using an up-to-date email client and web browser. Don't use an ancient, no-longer-updated email client. (You'd be surprised how many people do.)
So yes, it is safe to use the preview pane, and may you enjoy the productivity boost it gives you! We highly recommend giving Gmail's preview pane a spin.