diff -up dovecot-2.3.21/dovecot-pigeonhole/src/lib-sieve/plugins/include/cmd-include.c.ph_optglob dovecot-2.3.21/dovecot-pigeonhole/src/lib-sieve/plugins/include/cmd-include.c
--- dovecot-2.3.21/dovecot-pigeonhole/src/lib-sieve/plugins/include/cmd-include.c.ph_optglob	2024-06-04 09:11:28.514189662 +0200
+++ dovecot-2.3.21/dovecot-pigeonhole/src/lib-sieve/plugins/include/cmd-include.c	2024-06-04 09:18:23.219809778 +0200
@@ -368,11 +368,13 @@ static bool opc_include_dump
 		return FALSE;
 
 	sieve_code_descend(denv);
-	sieve_code_dumpf(denv, "script: `%s' from %s %s%s[ID: %d, BLOCK: %d]",
+	sieve_code_dumpf(denv, "script: `%s' from %s %s%s%s[ID: %d, BLOCK: %d]",
 		sieve_script_name(included->script), sieve_script_location(included->script),
 		((flags & EXT_INCLUDE_FLAG_ONCE) != 0 ? "(once) " : ""), 
 		((flags & EXT_INCLUDE_FLAG_OPTIONAL) != 0 ? "(optional) " : ""),
-		include_id, sieve_binary_block_get_id(included->block));
+		(included->block == NULL ? "(missing) " : ""), 
+		include_id, 
+		(included->block == NULL ? -1 : sieve_binary_block_get_id(included->block)));
 
 	return TRUE;
 }
diff -up dovecot-2.3.21/dovecot-pigeonhole/src/lib-sieve/plugins/include/ext-include-common.c.ph_optglob dovecot-2.3.21/dovecot-pigeonhole/src/lib-sieve/plugins/include/ext-include-common.c
--- dovecot-2.3.21/dovecot-pigeonhole/src/lib-sieve/plugins/include/ext-include-common.c.ph_optglob	2023-09-14 15:18:26.000000000 +0200
+++ dovecot-2.3.21/dovecot-pigeonhole/src/lib-sieve/plugins/include/ext-include-common.c	2024-06-04 09:10:45.187823805 +0200
@@ -693,6 +693,25 @@ int ext_include_execute_include(const st
 	}
 
 	ctx = ext_include_get_interpreter_context(this_ext, renv->interp);
+	if (included->block == NULL) {
+		if ((flags & EXT_INCLUDE_FLAG_OPTIONAL) != 0) {
+			sieve_runtime_trace(
+				renv, SIEVE_TRLVL_NONE,
+				"include: skipped include for script '%s' "
+				"[inc id: %d, block: NULL]; optional and unavailable",
+				sieve_script_name(included->script),
+				include_id);
+			return result;
+		} else {
+			sieve_runtime_trace(
+				renv, SIEVE_TRLVL_NONE,
+				"include: unavailable script '%s' "
+				"[inc id: %d, block: NULL]",
+				sieve_script_name(included->script),
+				include_id);
+			return SIEVE_EXEC_BIN_CORRUPT;
+		}
+	}
 	block_id = sieve_binary_block_get_id(included->block);
 
 	/* If :once modifier is specified, check for duplicate include */