The Diplomacy interface is primarily used for reviewing and changing the levels of diplomacy one maintains with one's fellow players. It also contains access to the Message Log. Additionally, one can change player race starmap colors from here.
Planets.nu has several different levels of Diplomatic Status which can be set from the Diplomacy screen:
When you send an ambassador to another race it is an indication that you wish to open communication with them for diplomatic purposes. Once you send an ambassador to another race they will be able to send messages to you without the normal 1 turn delay. Any messages they send will be relayed through your account email address.
You will not be able to send immediate messages to them until they send an ambassador to you.
When you grant safe passage to another player you will transmit information about all of your minefields and their ships will not hit your mines when passing through them, nor will your web mines drain their fuel tanks. By granting safe passage you will not be able to sweep the minefields of the opposing player. You are not able to fly through the opposing player's minefields unless they also grant safe passage with you.
In addition, safe passage disables most of the aggressive actions that can be taken towards the other player. Your ships, planets & starbases will not attack theirs (overriding the Primary Enemy setting and the Kill mission), except in response to an attack. It should be noted that ground attack, Imperial Assault, Pillage Planet, Plunder Planet and Rebel Ground Attack are not disabled by safe passage, or any other level of Diplomatic Status.
Safe passage includes Send Ambassador.
When you share intel with another player you will transmit the location (only the location) of all the planets that you currently own and the location of all of your ships. You will also transmit all ship and planet information from other races that you know about unless you are already allied with the other race.
In most cases, you will not transmit information gained from sharing intel with other races, but accidents do happen. This limit is due to the Strategic Information Sharing Act of Year 0011.
Share Intel includes Safe Passage and Send Ambassador.
A Full Alliance works exactly like Share Intel except that you will send all information (including the Friendly Code) about your planets and all information (except the Friendly Code) about your ships. Detailed information about combat (VCR) is also shared.
Full Alliances can combine their scores to win games where diplomatic victories are permitted (the Diplomatic Planets win condition ).
Full Alliances only begin to function once both parties have given a full alliance to each other. Once this happens, the Full Alliance is announced to all players via the in-game "Public Board", which can also be seen in the game's activity feed. If the Full Alliance is later broken, that information is made available to all players in a similar manner. This is the only diplomacy status information that's made available to all users.
Full Alliance includes Share Intel, Safe Passage and Send Ambassador.