What may happen if the line length of your electronic cover letter exceeds 65 characters?

The answer is: Your cover letter might not be read or with much difficulty, thus, it won't be taken into account.

Explanation:

Your cover letter is really important when you attend your job, although electronically might be a bit more informal than a physical one, you need to make sure to stay short but concise, in those 65 characteres be sure to include who you are and why are you capable of having that job, Avoid being repetitive and go to the nitty-gritty.