There are two types of email formats that could be giving others the wrong impression of you. One is the single large block of copy; the other is the one including too much detail.
Here are the perceptions others get when receiving either one of these messages.
Typing one large block of copy is the equivalent of rambling. Being unable to separate your thoughts is quite frustrating for others. They will think you'll also speak in a rambling manner making them less likely to agree to meet with you.
65%+ of all emails today are opened on mobile devices. Most people hate scrolling through lengthy emails. Having to do so makes them feel you are inconsiderate of their time. When a lot of information needs to be shared, create a document to attach, only referencing 2-3 main points in the email.
Making each thought a separate paragraph, using numbers or bullet points, and including more white space makes it easier for 1) you to clearly communicate; and, 2) others to follow along and reply efficiently.