While ThomasOwens leaves a fantastic answer here, I have a differing opinion to the question asked, however I also won't say he is incorrect. After all, as he had already pointed out, the diagram should have maximum communicative benefit while staying as focused as possible.
There are a number of types of Deployment diagrams that one might want to make and each kind can be used to show a unique view of the system. Deployment diagrams can be used to show the physical manifestation of components in a system, a specification for artifacts to deployment targets, and yes even the physical or logical infrastructure of a system.
External services and FTP connections like Thomas Owens said MIGHT be important to communicate the logical infrastructure of your system (Eg. firewalls, FTP client software packages, etc...) however unless you considered these services or FTP drop locations as part of your logical infrastructure then I wouldn't show them as Nodes in your diagram. What I typically do is draw the border around my logical infrastructure then have a nebulous box just to put a name to something on the other end of that communication path.
I prefer however to show external services and the like in component diagrams. Components within a system typically operate within a greater system (Eg. Enterprise, Internet, Client Intranet over VPN, etc...) so I view elements like this as external components with a well defined interface. Since components can both Provide and Require interfaces to other components, one really should demonstrate external system component interfaces so that it is clear what YOUR component Requires. Documenting this allows Architects and Developers to more easily reason about the components they must build.
In the end though, there are no hard and fast rules for these kinds of things, and as always, stay within the loose guidelines where you can until they don't benefit you. A diagram should be a tool to aid in the communication of a system so the most important thing is to ensure that your audience finds all the answers they need and gets everything they want out of your diagrams.