The railway mail service was...
The state’s first international RPO, the St. Vincent & Winnipeg, initiated service from that Kittson County town to Canada in August 1881.
My great uncle, Charlie Fitzpatrick, and later his brother, Dick Fitzpatrick, both worked at the St. Vincent depot, and one of their daily responsibilities would be to switch out the mailbags, both incoming and outgoing. Some of the sorting for the various towns on the particular RPO was done on the trains, separating for each town they were responsible for. Once delivered to St. Vincent, for example, then the town's postmaster would do the final sort for each postal customer.