Email is ubiquitous, and many of us send and receive multiple hundreds per day. But there are plenty of ways to get email wrong, and in doing so, to offend, to brand yourself or your business badly, or to even kill a deal or end a career.

Of all the email mistakes you can make, I've asked customer service expert Nancy Friedman to weigh in this week with the five her organization sees most in its research.

1. Poor grammar and spelling

Yes, we all make occasional mistakes, particularly when emailing late at night (which highlights yet another reason you shouldn't be sending professional email late at night). But poor grammar and spelling leads the pack of annoyances and shouts to the recipient that you didn't proofread nor did you use spell check. "Your" vs. "you're" and "their," "there" and "they're" are the most frequent offenders, along with "too," "to" and "two." Context is important as well, especially when you are trying to make a good impression. (Think job applications, cover letters, and anything you intend to send to a manager or the boss.)

Quick short cut if you're unsure of a usage question and pressed for time: changing the wording may be faster and easier than looking up the differentiation between words such as "affect" and "effect." But for the longer term--vow to increase your skill set to be sure your words of choice are correct.

2. Wrong subject lines

We've all been guilty of this. When an email string winds on to the point it's entered new topics, change the subject line before you respond. Or at least alter the end of the subject to make it clear the topic you're addressing is new (i.e. Here's your proposal--and next week lunch). It's a courtesy step, and will make the message easier to find.

3. Brevity is a virtue

Long messages are an email etiquette sin. Worst case, you should at least give the recipient a heads up: 'Long email'. Or you could use an attachment. As a rule of thumb, your signature line should be visible at the bottom of the screen without scrolling.

4. Not responding quickly (or responding too quickly)

As a service provider, if your fast response makes it clear you are online fairly close to 24/7, you may be inadvertently training your clients to think of you and use you that way. In some settings it may be more professional to time your responses for the start of the next business day, regardless of when they were written. But during working hours, if you can't get back immediately, replying with "message received; will reply shortly," particularly if the recipient is important, is a way to let senders know their note has arrived. It's a neighborly and "nice" thing to do, particularly if it will take you a little while to respond.

5. Reply all

In the early days of email, reply all seemed like a great way to strut your stuff in front of everyone on the list. But no more. A group email is not a chat room and you should not treat it is as such. Furthermore, as the sender of a group email, be sure to gather the names of the recipients in a way that avoids revealing the names and email addresses of everyone on the list. Even major corporations or publications have made the mistake of revealing the personal email addresses of private recipients to all.

Furthermore, many of the greatest email gaffes in history have occurred when someone either forgets to remove a prior conversation thread (which may contain personal or confidential information) or accidentally sends an angry or highly personal response intended for a single recipient to "all."

If you've stepped into these typical blunders, you're in good company. Email mistakes occur at least now and then for us all.

However, as you focus on better clarity and etiquette, consider another aspect of email as well: Should you ever really consider your electronic messages private? If you'd be uncomfortable with your message being seen by your boss (or your mom) or in a court deposition (yes, it's happened to many), perhaps you should examine the wisdom in sending the message in the first place. Particularly in the era of corporate email hacks, Wikipedia leaks, or the prevalent gaffe of walking away from a machine and leaving your private email or IM program logged in--if the email is too personal, too gossipy or is simply distasteful, perhaps you should question your motives for sending the message at all.