Change to:
pass in on $ext_if inet proto tcp to $ext_if port $webports rdr-to $webserver pass in on $ext_if inet proto tcp to $ext_if port $email rdr-to $mailserver pass in log on $int_if inet proto tcp from $int_if:network to $ext_if port $webports rdr-to $webserver pass in log on $int_if inet proto tcp from $int_if:network to $ext_if port $email rdr-to $mailserver match out log on $int_if proto tcp from $int_if:network to $webserver port $webports nat-to $int_if pass on $int_if inet proto tcp to $webserver port $webports match out log on $int_if proto tcp from $int_if:network to $mailserver port $email nat-to $int_if pass on $int_if inet proto tcp to $mailserver port $email