my Sieve filter setup (i.e. how I block spam)

filters.siv

require ["reject"];
# rule:[Reject emails to any aliases that have started to receive spam]
if address :localpart "to" ["alias_1", "alias_2"] {
    # The multi-line string lets me include a newline to separate my message from the message the mail server starts the rejection email with
    reject text:

To prevent spam, all messages to this address are automatically deleted. See https://mileskrell.com for current contact information.
.
    ;
}