This may sound somewhat pedantic, but most people online have experienced this to some degree or another.

Writing skills in the general Internet populace stink.

This means you can make yourself look even more intelligent and thoughtful than you are by writing well. Good writing is not difficult and requires only grammatical sentences and proper spelling. You do not need to be a professional writer or be able to make words flow easily and sensibly off the fingertips.

You should also follow a few basic rules when writing email:

Do not use all capital letters for more than a word. Capitalization online indicates a raised voice (i.e. yelling), something that is often considered very rude.

Insert a blank line between paragraphs. This makes reading your messages so much easier. This should be pretty obvious, though it seems to continue to be an issue with some people that send email.

Surround URLs with angle brackets to avoid problems at line breaks.

Do not use text styles (like bold or italic) or text colors in email. Many people will not see them and may even see HTML tags instead. This is beyond the dangers that exist by using HTML email. Use plain text email only.