Q: How much can you customise a communication piece?
A: As much as possible.
Try to blend in with the colours of the inbox if it is an e-mailer you are sending. It makes for a pleasant read and chances are that the recipient just might read the first few lines instead of clicking the delete button. It helps if your logo blends well with the colour of the inbox too. And if it is placed on the top. Instant recognition. And then instant recall... "I remember this mail from (enter your company name here)".