If you've ever found yourself about to press send, but you get a feeling in your gut that is telling you not to, listen to your gut. There's a reason why it's speaking to you.
Perhaps you find yourself thinking these thoughts:
"This is probably going to tick him off."
"This will put her over the edge."
"I hope my client doesn't misinterpret the pricing I've laid out for them."
"I hope they read through this twice before responding back to me."
If you've ever had these or similar thoughts, don't press send. Instead, have a voice-to-voice conversation regarding the matter by picking up the phone or visiting the person face-to-face.
Another option for those emails that might be a bit "edgy," is to put them in your drafts folder overnight. It's amazing what rest can do for your mind and your gut.