The header of your mails is what will "dress" them. You wouldn't show up for a business meeting in the simplest device, would you? In the same way, the dresses of which you will put your professional letters will be essential.
These tips will help you to better match your letters.
1. Dress your mail up and down
In a letter, you will have the body of the message, in the middle, but also the header and possibly the footer.
All these areas must be clearly identifiable at first glance.
Out of the question to see a foot, with for example the address of your seat, to stick to the signature, without distinction, to the point of resembling a postscript.
Respect the different areas and mark their separation, with sufficient white space, a line, or color choices.
2. Go til the borders
Think of the outer edges of your page as a frame, and put some color on it.
Visually, this attracts the eye of the recipient: your mail will not get lost in the mass of mail received, it will immediately stand out.
This technique assumes of course a color impression: a black frame would evoke too much invitations far less pleasant to receive.
On the other hand, all the techniques of color are usable, from the simple monochrome border to the gradients, passing by the reasons.
3. Review your geometry in opposite angles
For a simple but elegant design, you can always count on geometric shapes.
Calculate how you can insert them in a higher angle and a lower corner of your mail without losing too much space on the body of the letter.
A symmetrical effect would be here unwelcome: you will have to compare the advantages of opting for a larger format design at the top or bottom of the page.
You will notice that this technique, which adds a little life and dynamism to the dullest mail, can also be declined: