Board Thread:Episode Discussion/@comment-14138255-20161106163624/@comment-28345522-20161110135025

Mail doesn't have to be sent by airship, Ironwood could've sent it by boat. While by air is leagues faster than by boat, it's still reliable mode of transport that has not been restricted by the councils. With modern day ships, Ironwood and Tai could have a conversation then send the robot arm all within a month.

This of course doesn't account for how often ships are being attacked and whethet the show will give some other answer.