When is it appropriate to use e-mail rather than the postal service to send a letter of complaint?

When the company lists it's email on it's site, open for questions, suggestions and complaints. 

The answer is a hope this

A. they give the reader hope. if the whole book was dark & unhopeful it’d be a little less interesting, little moments make it more interesting to read because then you want to know what happens. if it’s all dark there’s no point in reading if you already know the outcome of it.