Add to the rule set:
rdr on $int_if proto tcp from $int_if:network to $ext_if \
port $webports -> $webserver
rdr on $int_if proto tcp from $int_if:network to $ext_if \
port $email -> $emailserver
no nat on $int_if proto tcp from $int_if to $int_if:network
nat on $int_if proto tcp from $int_if:network to $webserver \
port $webports -> $int_if
nat on $int_if proto tcp from $int_if:network to $emailserver \
port $email -> $int_if