Perhaps there could be a building implemented named the Trade Depot. The higher the level, the more resources you can send and receive at a given time, and the more often you can do so from a single player.

Level 1 could be 100k between two players and a 2 hour wait time between those players
Level 2 could be 200k and a 1:45 wait time
Level 3 could be 300k and a 1:30 wait time
...
Level 5 could be 500k and a 1:00 wait time


Then as one gets a higher level you can trade with more players at once, the cool down time between the two players lessens, and the amount of resources sendable and receivable would grow at larger rates.

If player 1 has a high send capacity and player 2 has a low level Trade Depot, then there will be a number somewhere in the middle that limits smaller players from receiving too much res.

If there is a building that limits the amount of resources that can be traded at a given time, it will be more frustrating to send res and more likely that the players will not feel like it.

Players could also be limited from receiving too much resources at a given time.

What about some sort of proxy? You send the resource of choice to a given non player planet and, as both parts arrive, they receive their share. That is easily automated to deny trades against any given rules and would offer secrecy to both parts. I believe it could work with a trade mission specifying the other part and the resource you expect to receive.

This has been an issue in the past and the rule hasn't really worked in a lot of cases.
There is another option though: Make it possible for every player to receive a set amount of each res ONCE each week?
It doesn't matter who sends it, if they are given the res once it's over for that week.
The amount should be reasonable;not too much but not too low either.
It should be a set amount, not dependent on level of mines or hourly production.
Also it doesn't matter if said player is given less than the set amount, once the transport has been completed he or she will have to wait for 7 days before being able to get a transport again.
Concerning collecting the DF for the attacker and transporting it to him; maybe another option that registers it and posts on socreboard for all to see?
It's not perfect ,i know. But it's an idea...

I like the tag system, but don't forget to include a tag for moonshot repayment. Not all players are in an alliance, so repayment is hard to do without breaking the current rules. At about 4.2m resources per shot this can get very expensive if many attempts have to be made.

I think the reason none of the above ideas have been implemented, is that the reality is a bit more complicated. It’s worth noting that a lot of milking cases actually involve attacks rather than transport (res raided off a moon, fleet crashing, creation of dummy accounts near one’s own colonies, etc.) Transports have an important place in interactions between teammates, and I think restricting them is generally a mistake. A tag system raises a number of logistical issues, though is probably the best way listed here to monitor things if a change were deemed important.

I’ll also say for everyone’s benefit to try to assuage any worries: Transports are always ok as long as they are trades. Moonshots count as trades, and simple repayment of ship cost for moonshots is always fine.

There are a few other things like this; for example, returning some fraction of the DF or resources raided after a crash (fleeters sometimes do this to encourage rebuilding, or even, occasionally, to protect alliance mates). This is another thing that might seem suspect if we only framed things in terms of transports, but is also fine. Generally as long as a transport is only compensating for a loss that occurred at the compensating player’s benefit, it is fine. The important thing is that the action when viewed in context does not constitute pushing or pulling (especially pushing).

Takeaway: Transports are important, especially for small growing players trading resources or moonshots, though established players and ruby buyers might no longer have as great a need for them, or forget how important they can be for smaller players. It’s not as if transports are the only, or even the most frequent, subject of milking violations. Generally speaking, if you are an honest player playing your own account to your own benefit, you needn’t worry.