Many email users have more than one email account. Do you care which one they use to receive your emails?
You know not all the emails are monitored equally even if they belong to the same user.
Some email addresses are checked more often than others. Some accounts are relatively free from spam while others receive so much promotional emails that your message simply disappears in the countless flow of ads.
So, the important question is how do you persuade your prospects to give you the email address they treat better?