Can snails swim?

I know that snail mail moves along at its own pace. But I wonder, do these snails have to swim across open water, in the event of severed political relations between 2 countries? Specifically, is there any rational explanation for the fact that in my mailbox yesterday, I received a postcard from Cuba...which was sent to me by a travel companion while I was still in Cuba 385 days ago? If it takes this long for a card with 8 words, how long would an actual letter take? Can't they send bags of mail periodically with the Americans who come to Cuba via Mexico, Jamaica or Canada? Since there is no postmark, perhaps the snail had to evade the coast guard and sneak ashore in Georgia or something.