When we think of keyword research we usually don't think beyond search engines. However, keyword research has applications beyond SEO and PPC. Another online marketing discipline it applies to is email marketing -- albeit with a different angle.
Keywords are everything to email marketers. Choosing the right words to put in an email message can make the difference between campaign success and miserable failure. Keyword research  is applicable to nearly all aspects of an email message:
It starts with the sender. You don't want your email to be seen as coming from an anonymous person or a source that isn't trusted. Putting the right sender name in your email software is a vital aspect of crafting an email marketing campaign.
Most email marketers go for branded keywords here, usually representing the organization the email is sent from. An email from Nike will be treated differently than one from John Doe. You can choose to stick with your organization's brand or try some variations and related phrases.
Probably the single most important aspect of an emailing is its subject line. This is what makes a recipient open or discard the email. A poor subject line can make all your efforts go to waste, while a good one can propel your campaign to the heights of marketing success -- or at least an upwards-pointing graph on your management reports.
So it's vital that you construct a subject line that contains the right words and phrases to convince the recipient that it's worthwhile opening and reading the email. You need to include the right trigger words to persuade a recipient to open that mail.
Persuasive keywords like "cheap," "free," "value" and "bargain" are common here, but you shouldn't abuse them too much. The trick is to find the right mix of persuasion and value, without overdoing it, to make a recipient feel that opening your email is worth their time and your message isn't just another pushy sales pitch.
There's a whole host of tried and tested keywords  and phrases for email marketers to choose from, but a seasoned email marketer won't be limited to a fixed set of words. Like with many online marketing disciplines, testing is key. Try out different ways of phrasing your email subject line , different trigger words and persuasive elements, and don't ever be satisfied with your results. There's always more to be squeezed from your campaigns.
So you've got a recipient to open the email, now you need them to read it and, hopefully, perform an action. The "above the fold" mindset is not unique to newspapers and conversion rate optimizers -- it's an absolutely vital aspect of email marketing as well.
Like with CRO, in email marketing you need to get your message across repeatedly and with the right persuasion elements. The difference is that with email you have much less time and space to do it with. That's why you need to work hard at including the right tone of voice, the right persuasive elements, and the right calls to action.
Again, it's wise to use synonyms and alternative phrasings in your email message. Experiment with related keywords and varied calls-to-action, or even with entirely different content -- you might be surprised by the results.
The trouble is of course that the words people usually respond best to are also the same words spammers use in their emails. Words like "cheap" and "free" are strong persuasive words, yet they also raise flags on spam checks.
You need to make sure your message doesn't end up in your recipients' spam folders, which means you need to apply restraint when using potentially spammy persuasive words. You can check whether your message is likely to be flagged as spam with tools such as Sitesell's spamcheck .
Try using synonyms for your persuasive words and formulate phrases in different ways, and always test, test, and test some more. You can run different versions of your campaign simultaneously to try out variations and find the best performing email message. You can then use this as the starting point for your next campaign.
There's a lot more than just spam words that comes in to play when a spam filter determines to allow an email in to the inbox or to junk it, but choosing the right keywords and avoiding abundant use of spam words are definitely key elements.
As you can see the focus of keyword research in email marketing is more limited than that in search marketing, but it's no less important. And you can use the same keyword research tools  as you do for SEO and PPC -- after all, if a particular word or phrase gathers a lot of searches, chances are it might work in an email message as well.
Barry Adams is a senior internet marketer at Pierce Communications.