Non mischiare JOIN espliciti e impliciti. In realtà, non usare JOIN impliciti.
Ecco la query che desideri:
SELECT
*
FROM
table1
INNER JOIN table2 alias1 ON table1.id_table3 = alias1.id_table3
INNER JOIN table2 alias2 ON table1.id_table4 = alias2.id_table4
INNER JOIN table3 ON table1.id_table3 = table3.id_table3
INNER JOIN table4 ON table1.id_table4 = table4.id_table4
INNER JOIN table5 ON table1.id_table5 = table5.id_table5
INNER JOIN table6 table6alias ON alias1.id_svw_uebertragungsweg = table6alias.id_svw
LEFT JOIN table2 alias3 ON table1.table1_id_table3_sender = alias3.id_table3
WHERE
table1.id_table3 != 0
AND ( table1.id_usr = 0 OR table1.id_usr IS NULL )