If you're brand spanking new to the professional world, there are hundreds of perfectly good lists of email etiquette tips out there, reminding you to do basic things like proofread, keep it brief, and use a short, sensible subject line. This list is not one of those.

This list is for people who have been firing off emails for years, who have not only long ago banished excessive exclamation points and long-winded asks, but have even mastered the dark art of the subtle email clapback and figured out how to pack even complicated communication into a tight, five-line missive.

But even email pros sometimes make mistakes. They're not just the "reply all" disasters of the less experienced (or less cautious). Instead, they're usually errors of context, timing, or empathy, like these below, that can lead to misunderstandings, hurt feelings, or blown deals.

1. Consider the medium.

Sometimes the problem with your email is that it is an email. Given the ease of electronic communication (and the growing incidence of phone phobia), even the smartest among us often unthinkingly start tapping away at our keyboards in response to any work or interpersonal conundrum. But emotional deftness is nearly impossible over email, which makes it inappropriate for more delicate discussions.

As tech commentator Clay Shirky has said: "When you communicate with a group you only know through electronic channels, it's like having functional Asperger's Syndrome--you are very logical and rational, but emotionally brittle."

Consider, too, that you're also less likely to persuade over email. One study found that you're 34 times more likely to get a yes when you ask someone the same exact request in person. So, before you start worrying about more subtle email etiquette errors, ask yourself this big question: Should you be sending an email at all? Might a phone call or face-to-face chat be more appropriate?

2. Write with your audience in mind.

Google "email etiquette" and you'll get a million lists of dos and don'ts. What almost all of them fail to mention is that how you write your emails very much depends on the intended recipient. Overly broad rules, like "keep it formal," aren't particularly helpful when some sections of the professional world are much more relaxed. A better rule for advanced emailers is "know your audience."

"Our email greeting and sign-off should be consistent with the level of respect and formality of the person you're communicating with. Also, write for the person who will be reading it--if they tend to be very polite and formal, write in that language. The same goes for a receiver who tends to be more informal and relaxed," workplace expert and author Lindsey Pollak has previously told Inc.com, for example.

3. Balance productivity with politics.

Who to include in a group email is another area where common email etiquette advice often goes wrong. "Spare people's inboxes and leave off the head honchos for routine matters," these lists often instruct. Which is usually great advice. As a matter of productivity, you should aim to include the minimum number of people possible in an email.

But productivity isn't the only consideration. Politics matters, too. You may know that you didn't include that one guy because you were trying to spare his inbox, but he may take it as a sign you were intentionally sidelining him. If you have the wrong kind of boss, leaving her out of the loop, even if no action is needed on her part, will appear more like a cover-up than time-saving brilliance.

Yes, efficiency is a laudable goal, but here in the real world it needs to be balanced against people's perceptions, personalities, and sometimes irrational fears. The smartest emailers keep that in mind.

4. Ensure all introductions are double opt-in.

This one particularly applies to emailing influencers, executives, and other bigwigs. Do these super in-demand people love to meet new people who will enrich their lives and their businesses? Of course they do, but only if they agreed to sharing their much-sought-after contact details and scarce time first. That's why opt-in introductions are so essential.

Top VC Fred Wilson has explained this crucial bit of advanced email etiquette succinctly on his blog: "When introducing two people who don't know each other, ask each of them to opt-in to the introduction before making it." It's a rule he--and other ninja-level emailers--follow religiously.

5. Be careful about when you hit send.

The advantage of email is that you can send it any time that is convenient for you and they can respond whenever is convenient for them, right? Actually, no. The smartest emailers know that while the timing of an email might appear irrelevant on the surface, in many circumstances it really does matter (and not just if you're sending a marketing email and trying to catch potential customers in a receptive mood).

In many industries and offices, the unwritten code of communication is that email must be answered as soon as possible. Sending one creates an immediate demand on the recipient (even if that's just the mental energy it takes to decide to flout convention and ignore an inbox ping). That's particularly true if you're a boss emailing a subordinate or emailing someone after hours.

"Just because you've written it now doesn't mean it needs to be sent at this exact moment. Delaying the send is one of the most powerful and underutilized tools of emailing," writes Amber Rae in Fast Company. "Evaluate whether or not the message is urgent and needs to be replied to immediately. If you're cleaning up your inbox during your scheduled time, fire off the messages that are urgent and consider sending messages in the morning."

That sets up a more human emailing rhythm and a more reasonable expectation for the time scale clients or colleagues need to reply.