Q:
2 Bug (Hints Menu) Blocks Achievements
For the Mailbox is full hint, try deleting all mail messages from ANet or NPCs. Not the Heart messages or the Green Star messages, just the ones with the envelope icons. Then have guild mates send you mail. That is was I had to do. It has been somewhat documented in other bug threads on the Hints Achievement.
For the Finish Opponent hint, I got nothing. I went to the Mists and did the little training island and got the achievement some time in the last 2 weeks. not sure if it bugged since then.
i finish mail hint before about 2h and works well, delete all mesages and make guild send you 11 emails, with 11th its show red mailbox and shortly (few sec.) hint pop up
i dont know about F in www, i finish this long time ago