There is no shortage of list that will give you the rules, etiquette or do's and dont's of e-mail... here is my short list of ‘When Sales People Shouldn't Use E-Mail'.

Sarcasm - Sarcasm doesn't work with e-mail at the best of times... with a client it will be a disaster.

Negative Reply - If you need to answer an e-mail with any negative connotation... like not being able to deliver what the client wanted, an important shipment will not make it on time, the pricing you agreed upon has increased or your meeting time needs to be moved... pick up the phone and talk to them.

Jokes - clients will send you jokes and NSFW pictures... it is not an invite to share what you find funny or sexy.

Sensitive Information - Don't send an e-mail to a client you wouldn't want your competition to read.

Hitting reply is too easy, calling a client to reply to their e-mail is often more effective, more personal and will help you gain the trust you are looking for.

 By Sean