diff --git a/setup/mail-postfix.sh b/setup/mail-postfix.sh
index 972d9f32..efc833db 100755
--- a/setup/mail-postfix.sh
+++ b/setup/mail-postfix.sh
@@ -171,6 +171,11 @@ tools/editconf.py /etc/postfix/main.cf \
 
 # Postfix connects to Postgrey on the 127.0.0.1 interface specifically. Ensure that
 # Postgrey listens on the same interface (and not IPv6, for instance).
+# A lot of legit mail servers try to resend before 300 seconds.
+# As a matter of fact RFC is not strict about retry timer so postfix and
+# other MTA have their own intervals. To fix the problem of receiving
+# e-mails really latter, delay of greylisting has been set to
+# 180 seconds (default is 300 seconds).
 tools/editconf.py /etc/default/postgrey \
 	POSTGREY_OPTS=\"--inet=127.0.0.1:10023 --delay=180\"