How can the emails affect the communication negatively?

Nonegative impact

some emails could not be understood because the weak language so in this case sender must verify and make sure the receiver understand the email

E mails can negatively affect communication when the message is misunderstood by either parties, when one of the parties does not master the language being used, when e mail is not clear, when in box is full and cannot be delivered and many other reasons 

Like any other communication tool:

- Unclear, wrong, or conflicting messages

- Wrong or selected receivers

- Language barrier for some receivers

Specific problem to emails is ensuring that the message is sent and received

Business emails should be short and crisp, and it should describe the subject very clearly and understandable with a right salutation. 

Well actually they can't. E-mails dont make damage by themselves, uncompetent people and intentional misscomunication on the otherhand are pretty capable of creating a little mess.

      That is why when refering to an e-mail that should be send to both high and low levels of management the visability will be limited thus hiding e-mail and protecting catastropic events blown out of proportions.

if don't know the rules to write an effective email.

When the content is not clear or carrying some possibly misunderstanding thoughts. 

Emails in all it's glory but beware.

You can never get that personal touch with an email.

For example the facial expressions , the voice spectra and the body language. Pretty much what you can determine in a personal encounter you cannot simply evaluate in a email!

You can never know the other person in the other end of nowhere or even if you know the person, you can't really know what feeling makes him answer or write in just this way just this time in a email.

Emails should be used just for answering direct questions and are not to relay on in business decisions or to send between each other just because we are to lazy to meet.

The best communication for a business or for all human is simply between four eyes or if you are more people, in a personal meeting with each other.

e-mail is one of the communication tools, it may be negative or positive according to how to use it.

But if we take much time in following e-mail, here it is negative.