Today I received an email from the firstname.lastname@example.org mailing list where a person asks how to set connection “sleep timeout” with postfix. This should reduce the amount of SPAM, since SPAM MTAs are less “patient” than regular MTAs. The reasons behind this approach were described here.
IMO the most reasonable value for this timeout according to the graph from MailChannels is 50 seconds. The reason is that most regular MTAs stay connected, but the majority of SPAM MTAs lose patience. Raising the timeout further might disconnect regular MTAs and has little effect on lowering SPAM MTAs disconnections.