This isn't going to be a terribly long diary, but anyone working CO phones tomorrow or working on the ground, there is a way to check if the Secretary of State has received your mail-in ballot.
If a CO resident mailed their ballot Friday 10-31 or earlier, it should should show up on the Secretary of State website here. They can enter their voter information, and the site will let them know if their ballot was received.
Here is an article at 9News with further voter information for CO residents.
Here is another article about turnout. More than 1.5 million CO voters have already voted. But 407,566 mail in ballots have yet to be received as of today.
Please let people know about this. If they have not received their ballot or it does not show up on the website, they can request a replacement ballot. Here is the website listing contact information for all County Clerk and Recorder offices in CO. That is who they contact to request a new ballot if theirs was not received or if they never got it in the mail. They can also drop off mail in ballots at their polling location until 7PM.
Please correct any factual errors. I am not in CO, but I was able to get this information from a friend.