Hint Completion Bug
My son and I just did the “inbox full” one this weekend – mine immediately granted the achievement, his did not.
Unfortunately (because this doesn’t apply to you, obv), a relog solved his issue and he was granted the achievement.
I mention this only to perhaps aid anet in troubleshooting.
I have played the game for five months now and nothing seems to work to solve this problem.
Had the inbox full several times and still don’t have the your inbox is full hint fulfilled.
I haven’t be able to get mine complete since … ever. I am updating, so I cannot say specifically which ones have me locked up, but … there are more than a few that I HAVE done but haven’t triggered the hint to be complete.