I assume you are looking for a stateless firewall filter and not an SRX security policy.
This would be the filter.
set firewall family inet filter RestrictSMTP term AllowSMTP from source-address 192.168.1.1/32
set firewall family inet filter RestrictSMTP term AllowSMTP from protocol tcp
set firewall family inet filter RestrictSMTP term AllowSMTP from destination-port smtp
set firewall family inet filter RestrictSMTP term AllowSMTP then accept
set firewall family inet filter RestrictSMTP term BlockSMTP from protocol tcp
set firewall family inet filter RestrictSMTP term BlockSMTP from destination-port smtp
set firewall family inet filter RestrictSMTP term BlockSMTP then discard
set firewall family inet filter RestrictSMTP term AcceptOther then accept
you would then apply this to the input of the interface where the subnet enters the switch.
set interfaces ge-0/0/0 unit 0 family inet filter input RestrictSMTP