$ man message-volume

Up to 20,000 Messages

The approximate message ceiling for a single campaign cycle. 10,000 contacts × 2-3 emails per sequence = 20,000-30,000 total messages. This is the volume that standard infrastructure (18-36 sender accounts) can handle in a 4-6 week campaign window.

Message volume determines infrastructure requirements. 20,000 messages across 18 senders at 25/day = ~44 days. 20,000 messages across 36 senders at 25/day = ~22 days. The relationship between message volume, sender count, and time-to-completion drives every infrastructure decision. If you need to send faster, add senders. Don't raise per-inbox limits.

I calculate message volume before infrastructure provisioning. Total contacts × emails per sequence = total messages. Total messages ÷ (sender accounts × daily limit) = days to complete. If the math says the campaign takes longer than 6 weeks with current infrastructure, I add sender accounts. If it completes in under 2 weeks, I might reduce senders to save cost. The math determines the infrastructure. Not the other way around.