Editing Tip of the Day: One Last Check

Today's tip was inspired by an email I sent to myself, full of notes and ideas for future posts:
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 Yes, that was supposed to be blog tip ideas, not top ideas.
Oops. I blame my phone keyboard and the late hour.
So today's lesson is, whether you're a new writer or a professional editor,
Always proofread your work. Especially if it's a professional email.
Thankfully this little mistake was easy to laugh off. But here are some things you definitely want to double-check any time you're sending an email or query:

All email addresses
The agent's (or other professional's) name. Especially if you're sending queries and cutting and pasting; there are too many horror stories of writers who forgot to change the name. Don't be that writer.
The formatting. Yes, it's boring. But you still need to follow directions.
Your subject line
​Your word count
Whether you were asked to send attached pages or pasted in pages
Your contact information. Wouldn't it be terrible if an agent tried to call you and you gave them the wrong number?
After you write a query, set it aside for a day if you can. Then read it aloud slowly, to make sure every single word is spelled correctly, means exactly what you want to say, and needs to be there. Voice in a query is good. Purple prose isn't.
Check again to make sure you've spelled the agent's name correctly. Do it.
If you're sending an attachment, make sure you actually attach the document. (I've never done that, I don't know why all my CPs are laughing at me right now...)
And lastly, if you're entering a writing contest, make sure to read the rules one last time before you hit send. You don't want to get your manuscript thrown out on a technicality when five minutes of extra attention could have prevented it, right? Which also means don't wait to submit until the literal last minute.

Anyone out there have suggestions of things to add to your manuscript or query's pre-flight checklist? Or cautionary tales of woe that you'd like to share? Our comments are always open. And as always, have fun editing!