Prereq: "3.3.17"
diff -ur --new-file /var/tmp/postfix-3.3.17/src/global/mail_version.h ./src/global/mail_version.h
--- /var/tmp/postfix-3.3.17/src/global/mail_version.h	2021-04-11 10:51:11.000000000 -0400
+++ ./src/global/mail_version.h	2021-06-13 15:05:09.000000000 -0400
@@ -20,8 +20,8 @@
   * Patches change both the patchlevel and the release date. Snapshots have no
   * patchlevel; they change the release date only.
   */
-#define MAIL_RELEASE_DATE	"20210411"
-#define MAIL_VERSION_NUMBER	"3.3.17"
+#define MAIL_RELEASE_DATE	"20210613"
+#define MAIL_VERSION_NUMBER	"3.3.18"
 
 #ifdef SNAPSHOT
 #define MAIL_VERSION_DATE	"-" MAIL_RELEASE_DATE
diff -ur --new-file /var/tmp/postfix-3.3.17/HISTORY ./HISTORY
--- /var/tmp/postfix-3.3.17/HISTORY	2021-04-11 10:48:36.000000000 -0400
+++ ./HISTORY	2021-06-13 14:58:13.000000000 -0400
@@ -23734,3 +23734,20 @@
 
 	Missing null pointer check (introduced: Postfix alpha) after
 	null argv[0] value. File: global/mail_task.c.
+
+20210601
+
+	Bugfix (introduced: Postfix 2.11): the command "postmap
+	lmdb:/file/name" handled duplicate keys ungracefully,
+	discarding entries stored up to and including the duplicate
+	key, and causing a double free() call with lmdb versions
+	0.9.17 and later. Reported by Adi Prasaja; double free()
+	root cause analysis by Howard Chu. File: util/slmdb.c.
+
+20210612
+
+	Support for Postfix 3.6 compatibility_level syntax, to avoid
+	fatal runtime errors when rolling back from Postfix 3.6 to
+	an earlier supported version, or when sharing Postfix 3.6
+	configuration files with an earlier supported Postfix
+	version. File: global/mail_params.c.
diff -ur --new-file /var/tmp/postfix-3.3.17/src/global/mail_params.c ./src/global/mail_params.c
--- /var/tmp/postfix-3.3.17/src/global/mail_params.c	2021-01-16 19:54:32.000000000 -0500
+++ ./src/global/mail_params.c	2021-06-12 11:05:25.000000000 -0400
@@ -815,6 +815,17 @@
     const char *cp;
 
     /*
+     * Ignore the Postfix >= 3.6 compatibility_level's minor and patch
+     * fields, to allow rollback from Postfix >= 3.6, and to allow
+     * configuration sharing with Postfix >= 3.6.
+     */
+    const char *compat_level_str;
+
+    if ((compat_level_str = mail_conf_lookup(VAR_COMPAT_LEVEL)) != 0
+      && ISDIGIT(compat_level_str[0]) && strchr(compat_level_str, '.') != 0)
+	set_mail_conf_int(VAR_COMPAT_LEVEL, atoi(compat_level_str));
+
+    /*
      * Extract compatibility level first, so that we can determine what
      * parameters of interest are left at their legacy defaults.
      */
diff -ur --new-file /var/tmp/postfix-3.3.17/src/util/slmdb.c ./src/util/slmdb.c
--- /var/tmp/postfix-3.3.17/src/util/slmdb.c	2017-02-18 20:58:21.000000000 -0500
+++ ./src/util/slmdb.c	2021-06-01 17:02:52.000000000 -0400
@@ -386,12 +386,16 @@
      * - With a bulk-mode transaction we commit when the database is closed.
      */
     if (slmdb->open_flags & O_TRUNC) {
-	if ((status = mdb_drop(slmdb->txn, slmdb->dbi, 0)) != 0)
+	if ((status = mdb_drop(slmdb->txn, slmdb->dbi, 0)) != 0) {
+	    mdb_txn_abort(slmdb->txn);
+	    slmdb->txn = 0;
 	    return (status);
+	}
 	if ((slmdb->slmdb_flags & SLMDB_FLAG_BULK) == 0) {
-	    if ((status = mdb_txn_commit(slmdb->txn)) != 0)
-		return (status);
+	    status = mdb_txn_commit(slmdb->txn);
 	    slmdb->txn = 0;
+	    if (status != 0)
+		return (status);
 	}
     } else if ((slmdb->lmdb_flags & MDB_RDONLY) != 0
 	       || (slmdb->slmdb_flags & SLMDB_FLAG_BULK) == 0) {
@@ -582,11 +586,15 @@
      * Do the update.
      */
     if ((status = mdb_put(txn, slmdb->dbi, mdb_key, mdb_value, flags)) != 0) {
-	mdb_txn_abort(txn);
 	if (status != MDB_KEYEXIST) {
+	    mdb_txn_abort(txn);
 	    if ((status = slmdb_recover(slmdb, status)) == 0)
 		status = slmdb_put(slmdb, mdb_key, mdb_value, flags);
 	    SLMDB_API_RETURN(slmdb, status);
+	} else {
+	    /* Abort non-bulk transaction only. */
+	    if (slmdb->txn == 0)
+		mdb_txn_abort(txn);
 	}
     }