Restrictions is limiting the Search Field by using Mathematical Operators, Expressions and Logical Operators.
This is the Search Restriction window.
Choose a Search Field to Restrict.
Filter the result to easier find the right one.
The Matematical Operator is the operation of the expression to generate a rule of which messages will be excluded.
Expression is the value which together with the Mathematical Operator will decide what's excluded.
Logical Operator only works if at least two Restrictions are added and decides if both of them will be restricted or just one at a time.
Logical Operators won't work as within brackets.