which could become annoying to some players when he get X mails a la "how are Y skills and do you want to trade him against X"
There is better way. Team could request to reveal skillset of player for themself by clicking a button. Owner could accept all requests automatically, accept them manually or deny all requests..
Then there has to be something which gives to these managers any feedback when this player appears on transferlist, because owner can get hungry if he will see a lot of interest for his player.
And that could be like pseudo-trading, but better than nothing.