It's often easier to hear a mistake rather than to read one, which is why reading out loud is such an effective self-editing tactic. Not only will you be able to catch errors of all varieties, you'll also be able to assess the tone of your email. For example, if you sound stiff and formal when you're reading it to yourself, it will come off that way to the potential customer too. Revise the text, and read it out loud again until it sounds right.
This isn't just a practice tip for those who are new to the sales world and sales emails. There are people who are 20-plus years into their career who still take the time to read their messages out loud before sending. Like proofreading, this is one of the copywriting skills that never expires.