OK. You all done it now.
Prepare for the tweet storm of what you absolutely need to do to scale up VBM (caution: pulling from the slide decks...)
First. Delivery standards are 2-5 days for First Class mail. set the right expectations by making sure dates/deadlines align:

Guidance from @usps is to advise voters to mail back the ballot one week before the due date to be certain. Are you mailing out ballots after that time? It may be setting up voters to fail if you don't allow various return options.

USE THE LOGO.
Period.
Seriously. Do it!!!! It increases the visibility of ballots in the mail stream.

Please don't just scale up your existing program & buy more envelopes. Implement best practices like using these great (FREE) templates from @civicdesign --be certain that you have it approved by @usps mail design analyst (FREE) to test for automation compatibility & usability.

Use green tag 191 for the same reason:

Some states are leading w reviewing & changing what a "postmark" means to include orange processing marks & Intelligent Mail Barcode (IMb)
OH, WA, IA, KS are a few.

Using labels?
Be sure that the voter address is the MOST PROMINENT part of label.
Affix it as straight as possible.

States moving to pre-payment of the ballot returns, be certain that you are talking about that with your local Election Mail Specialist & postmaster

Legislators, voters, administrators & USPS need to contemplate how their expectations jive with the New Reality of Voting by Mail--particularly in this COVID era

States need to provide available options in dropping off the ballot:

I cannot stress this one enough!!
Contact your local postal representative now & share:
Expected volumes
Deadlines
Design samples
Set up accounts
Discuss ballot returns: POB? Caller Svc?
Get your permits!