One of the most important aspects of e-mail is the header. The header in an e-mail tells the recipient whom the e-mail is from, when it was sent and what it's about. With the amount of email people receive everyday, it is important to get this right, so your message is not deleted unopened.

One-third of the people you are trying to reach will make a decision about reading your message based on how you identify yourself. Make sure it is clear who the email is coming from by identifying yourself and/or your company in the “from” field. This becomes very important when another company is sending your mail for you. Make sure that your name is the most prominent - if you are the one with the relationship.

The subject is your best opportunity to prompt recipients to open your email. The subject should be meaningful and should not sound like a make-money fast deal. Also, avoid the use of exclamation points, dollar signs, all caps and the word “free” because many anti-spam programs will tag your e-mail as spam.

Other considerations for the subject line include:

Be brief - the first 25 to 35 characters are about all that will get displayed on most email subject lines, so don't get cut-off.
Do not pretend - getting people to open your message under false pretences might help your open rate but it will not help you results.
Motivate them - make them want to open your message to learn more. A subject line is most effective when it can accomplish four things: solves a problem, solves that problem quickly, solves that problem for what appears to be a small or reasonable amount of money and creates intrigue.

E-mail Body

Most people read email in their preview panes, and they rarely maximise emails to full screen. Different email programs have different sized preview panes. Don't design your emails too wide. About 600 pixels wide is as far as you should go. Left-align your company logo. You don't want that to be hidden behind the preview pane somewhere. Your logo gives your email credibility.
Make sure the important content/message is within the preview pane to encourage the reader to keep reading.
Lead the way - people want information and they want it now. Remember that the email that you sent will be one of the many that your recipients receive. They will not waste valuable time trying to figure out what you are trying to sell.
Use clear a concise language to communicate with your recipients. Note that less is more in this case, as recipients will appreciate brevity over long-windedness when trying to get your message across to them.
Personalising each email with the recipient's name can increase your brand presence significantly, which translates to greater relationship building with your recipients and higher response rates. If you are using Swiftpage, simply add [[Salutation]] in the subject line. Eg. "[[Salutation]], here is our newsletter"
Use white space to break up text-heavy messages, making them easier to read. Never send one giant image as your message. It’s a good idea to work toward a 60:40 image-to-text ratio.
Use ALT tags on your images.
Colorful backgrounds raise a spam score greatly. A white background is the lowest scoring color within an email.
Include more than one opportunity to select a link.
Encourage readers to pass along your message to a friend. This is enormously effective.
Disclose your personal information such as a name and contact e-mail address. Assure the recipient that you are a real entity and that you welcome an open dialogue with them.
Make an offer to entice the reader to respond (i.e. free white paper, complementary consultation, etc.)
Give the prospect a reason to want to go to your web site for more information.