As one of the Eastern players in the other game, I'll give some feedback. This feedback will be about stuff which may or may not have mattered considering that your emails were not received. And it also may be stuff that you've already figured out, but which could benefit others.

You and I have a problem. I want Rumania. You probably don't want me to have it. Too bad. If you try to prevent it, you will have difficulties with Germany, Turkey, or Italy. If you move against Warsaw, you will earn my lasting enmity.

In 1901, Russia tends to be viewed as having a reasonable claim to Rumania, so it was correct for you to lay claim to it. Austria's feelings about you taking it will probably depend on whether he is thinking of working with you, and he may not have even decided yet in Spring 1901. He might like it for himself, but he would be ambitious to think it reasonable to actually get it, and he would need to feel confident that Turkey would back him up.

While there is a time and a place for brinksmanship, you really don't need it in 1901. Everyone knows that if Austria foils you from getting Rumania, and/or Austria moves to Galicia, it's starting a war.

My proclaimed intentions, from which I do not intend to waver unless I am threatened or attacked, are to seize Sweden and Rumania, and then remain passive and neutral for several turns.

Since diplomacy is a zero-sum game with limited territory, it's very hard to remain neutral. Russia especially is so big that it can't really remain neutral in the early game, especially not for a few turns (which is a massive amount of time). Everyone is asking who they are going to get centers from next, and who is going to help them do it.

Let's look at this from Austria's perspective. Who is he going to attack?

Germany or Italy? No, center powers attacking each other is a risky strategy. Positions in the center are harder to defend because of multiple fronts. Austria turning his back on the East will make him and the Balkan centers a very tasty target for a Juggernaught. Even if the East let him move West, taking over German or Italian territory will result in Austria being treated like a pinata mid-game.

So, Austria has to go after either Russia or Turkey. To go after Turkey, he needs either Russian or Italian help. Italy being unwilling to attack Turkey meant that the had to work with either you or Turkey against the other: a classic triangle. His initial email basically told you: work with me against Turkey, or I team up with Turkey and destroy you.

I realize that my move A Warsaw -> Galicia puts you at risk, but I need to make it to protect myself from your potential treachery

Typically Russia-Austria alliances work by keeping Galicia demilitarized. Since Galicia borders two Austrian home centers and only one Russian home center, it's more dangerous for Austria to let you in there than vice versa. No Austrian player will accept Russia in Galicia in Spring 1901 as anything other than a declaration of war. It crosses a Schelling point. (Similar logic applies to the Black Sea, which is why Turkey wanted to bounce you there.)

You don't need to go through Galicia to try to get Rumania. Remember, to keep you out, Austria has to weaken his claim to Greece (a neutral center that he badly wants), or work with Turkey. Yet if AT are working together, they can keep you out of Rumania no matter what. The way to get and keep Rumania is diplomacy. Autria's desire for Greece, or interest in working with you, are both reasons to let you have Rumania rather than jumping into an alliance with Turkey. (Austrian alliances with Turkey have drawbacks. Exhibit A: The current map.)

There are a lot of hidden norms and Schelling points in Diplomacy, and they must often be learned the hard way.