There is an WHERE option for each table. It selects rows that should be considered further in the process. So using the WHERE condition
… for that email column should do the trick in my understanding. All rows with a '@' in that column will be skipped. And this
.. will skip every row. All strings satisfy like '%' and thus no strings satisfy not like '%'
But be aware of this (Release notes for 8.0):
“The SQL_WHERE option in Data Sync is changed so that WHERE-condition is evaluated againstonly (before it was bothand (logically OR'ed)).”