The MTA's Sieve implementation supports the use of expressions in places where the base Sieve specification expects values. Such expressions can make use of a number of arithmetic and string functions and operators.
Note that because Sieve syntax uses square brackets to denote lists, the MTA's usual support for using square brackets to index into strings is not supported within Sieve filters; within Sieve filters, parentheses must be used rather than square brackets to index into a string, i.e.,
a(1) rather than
Note that the
imsimta test -expression utility can be used to test expression evaluation, and in particular Sieve filter expression evaluation.