American commerce with Santo Domingo would be further stimulated and strengthened by a tariff reciprocity agreement similar to the customs convention between the United States and Cuba. The mutual advantages of such an agreement would be enormous and the development of Santo Domingo would be effectively promoted. Closer relations would also be fostered by a postal convention applying the domestic rates of postage to all mail between the two countries, a good beginning having been made by a recent arrangement applying the domestic postage rate to letters between the United States and the Dominican Republic. The Dominican Republic has twelve ports of entry, but nine-tenths of the foreign commerce goes through the ports of Macoris, Santo Domingo, Sanchez and Puerto Plata. The first two supply the import and export requirements of the southern portion of the Republic, the other two those of the Cibao. The other eight custom-houses exist for local convenience and for the prevention of smuggling. This is especially true of the three along the Haitian frontier. In former years there was considerable smuggling across the border, as the import duties on certain articles in Haiti are much lower than in the Dominican Republic. Although the profitable smuggling business demoralized trade in those regions, the government did not interfere with it owing to the difficulty of policing the wild and sparsely populated border district. The American general receiver determined that the back door should be guarded as well as the front entrance, and formed a frontier guard which stopped contraband traffic, though at a heavy cost, for two brave American officials have been killed and three wounded by smugglers and outlaws, while fourteen Dominican guardsmen and inspectors have been killed and twenty-three wounded. The expense of the three frontier custom-houses is greater than the revenue they produce, but entries in Azua, Monte Cristi and Puerto Plata increased significantly after the frontier guard began its patrolling. Incidentally the guard has helped to keep the boundary line in place.