Horizontal antennas are not practical on a boat because there is a minimum height above ground clearance required and wires on a boat could be a big PITA. Imagine a wire breaking and getting caught in your prop.
I am not familiar with e-mail frequencies but I'm sure it is close enough to one of the HAM bands to work. Even better, get a HAM radio license
. They have e-mail frequencies, HAM radio is used by most cruisers I know and I never personally met anyone that used the Marine SSB
frequencies although I'm sure they exist. HAMs also have 'missionary' frequencies that you can call into as often as you like during the day. They will take your course, weather
etc. info and put you on Shiptrack.org. People on land can get on the internet
and go into shiptrack.org and see where you are with any messages you need to relay. They will also try to patch phone
calls for you or at a minimum, make calls for you. There are lots of other advantages of going HAM. I would rather have a hundred HAM's plus the Coast Guard know where I am if I run into trouble than the Coast Guard alone. They will pressure the Coast Guard to act.