c# - Sending serialized objects through the internet -

i developing program our organization. program (c# desktop program on windows 7) consists of 2 sub programs: "server" program , "client" program.

the "server" program installed in head office , receives info branches , in subject each employee trained in. has postgresql database end.

the "client" program installed in branches of organization (currently 9 branches), have file based database (undecided yet) , responsible gathering info got training in particular branch , in subject.

so, every day (give or take) every branch send training statistics main office's server program (? serialized objects), main office receive objects , store them in database , reply info, things "ok confirmed" or "yes, can that" or "no, refused". @ end of month head office computer process data , print statistics. real time communication between branches , server absolutely not necessary.

the question: given computers on internet , can't communicate each other directly (we have dynamic ip addressing in our country), how can serialized objects clients server , vice versa ?

my thinking can use email (send files attachments) or maybe on cloud file sharing program (dropbox or onedrive... etc). not expert programmer , know how these things done.

p.s.: cloud database not option. performance reasons + don't want our info in else's hands. way of communication ok because stuff signed , encrypted in transit.

it seems http server rest api suit quite good. need forward tcp port server outer internet (contact internet provider on matter if not sure).