The answer is...
A PASSWORD (or the sloppier, APASWORD)
A sequence spirals down and out, following the clock
Thanks to Namisca, but using the alphabet instead, the sequence spirling down and out/clockwise is
Q R S T U
P E F G V
O D A H W
N C B I X
M L K J Y
Starting with the first mail item a password you'll unlock
I don't really get this one, but 'A' seemed like a good place to start. Maybe mail is handled alphabetically? OP EDIT: as pointed out, "mail item" = letter.
Moving like a knight (not right) you'll want to first extend
Moving 2 left is the 'O', but it didn't help me so I ignored it.
Almost there, you look up (take a hint, man!) and then go home again
1 up is the 'P' and home again is back to the 'A'. I took both because they worked for me.
Fire two shots to the north to hit a curvy groove
2 up is the 'S' (which is the only reason I stuck with this because it fit the clue so well). Maybe take 2 of them because "two shots"? but that feels like overusing the two... OP EDIT: Indeed, "a curvy groove" refers to 'S'. Two shots is to take it twice.
Then like a bishop off to tea it's time to make a move
Thanks for whoever and the other guy for confirming that this is southeast. It's not clear how far to move, but it's either 'G' or 'W' and 'W' works better.
You stretch the furthest that you can to reach the leftmost end
Leftmost from the 'W' is the 'O'. I liked it. I kept it.
But when you're there, something nearby drives you round the bend
I really thought the 'N' fit the "bend" best, but rounding it is the 'C', and its head and feet are 'D' and 'L' which I didn't like. So I went round the 'P' to the 'E' and took its head and feet (in that order) - 'R' and 'D' OP EDIT: to be "driven round the bend" is to get angry, or "see red".
OP EDIT: There it is! Tall and upright, bold as it can be
Beside 'O' where we are now, the word "RED" can be seen vertically.
OP EDIT: You take its head, you take its feet! Now, listen close to me
Take the top and bottom of "RED" to get "R" and "D" in sequence.
OP EDIT: Hint meaning
The first letter of each line spells out 'ABCD' as a hint to get thinking about the alphabet as a sequence. The rest of the lines are just to be taken literally.
OP final comment:
I did tell you guys from the beginning that you would unlock 'A PASSWORD'. :)