This is an anecdote not data, but I've heard several USPS delivery folks mention that a lot of long-tenured drivers decided to take vacation and sick time when the lockdown started ramping up. This has caused other drivers to pick up the slack so there may be a lot of overtime getting paid out.
I can't get the numbers to add up here. Even with letters down, advertising down then their revenue should either be flat or have a slight increase based on my guesstimate for their increase in parcel business.