Artificial limits in the qmail system
The qmail system is able to handle messages of any size, addresses of any size, mailing lists of any size, and so on, except as limited by the available memory and disk space.
However, it imposes certain artificial limits:
qmail-lspawn silently limits the number of simultaneous local deliveries to 120. qmail-rspawn silently limits the number of simultaneous remote deliveries to 120.
qmail-queue rejects any message with an envelope address longer than 1000 characters.
qmail-lspawn truncates any overly long error report from a delivery program. It appends a note saying that it did so.