diff --git a/setup/mail-postfix.sh b/setup/mail-postfix.sh
index 6124d64e..3298bacc 100755
--- a/setup/mail-postfix.sh
+++ b/setup/mail-postfix.sh
@@ -60,11 +60,14 @@ apt_install postfix postfix-pcre postgrey ca-certificates
 # * Set our name (the Debian default seems to be "localhost" but make it our hostname).
 # * Set the name of the local machine to localhost, which means xxx@localhost is delivered locally, although we don't use it.
 # * Set the SMTP banner (which must have the hostname first, then anything).
+# * Set the default timeout for undeliverable e-mail to 1 day. The default is 5.
 tools/editconf.py /etc/postfix/main.cf \
 	inet_interfaces=all \
 	myhostname=$PRIMARY_HOSTNAME\
 	smtpd_banner="\$myhostname ESMTP Hi, I'm a Mail-in-a-Box (Ubuntu/Postfix; see https://mailinabox.email/)" \
 	mydestination=localhost
+	maximal_queue_lifetime=1d
+	bounce_queue_lifetime=1d
 
 # ### Outgoing Mail