merged upstream: https://github.com/svarshavchik/courier-libs/pull/10
from https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=824037

Date: 2016-05-11
Description: Use SOURCE_DATE_EPOCH for imapd version
 Use the environment variable SOURCE_DATE_EPOCH (if set) for imapd
 PROGRAMVERSION, to make the build reproducible.
 See https://reproducible-builds.org/specs/source-date-epoch/
Author: Alexis Bienvenüe <pado@passoire.fr>

Index: courier-imap-4.18.2/libs/imap/configure
===================================================================
--- courier-imap-4.18.2.orig/libs/imap/configure
+++ courier-imap-4.18.2/libs/imap/configure
@@ -18345,7 +18345,9 @@ courier)
 	;;
 esac
 
-date=`date`
+SOURCE_DATE_EPOCH="${SOURCE_DATE_EPOCH:-`date +%s`}"
+date=`date -u -d "@$SOURCE_DATE_EPOCH" "+%F %T" 2>/dev/null || date -u -r "$SOURCE_DATE_EPOCH" "+%F %T" 2>/dev/null || date -u "+%F %T"`
+
 
 cat >>confdefs.h <<_ACEOF
 #define PROGRAMVERSION "$package/${target_cpu}-${target_vendor}-${target_os}/$date"