All airlines, including cargo carriers who operate under part 121 have these limits:

Minimum 8 hours Rest in 24 (this is actually far more complicated...)
Minimum 24 hour rest period every 7 days.
8 Hours max flying in 24.
30 hours max flying in 7 days.
100 hours max flying per month.
1000 hours max flying per year.

Most pilots don't fly more than 85 hours month or you reach the 1000/year limit early (but some guys try to do that intentionally...free vacation the last few weeks of December)

I believe you can go 120/month and 1200/year in 135, not sure about their rest.