Nevermind I just bought it in-game

D.mail/schwermer/ensis shield/judgment counter count as autoskill.

It works like these,
-monsters deal 5k damages on you, if d.mail counter triggered, you will get 5k hp, so in the end your hp still the same.
-if monster deal damage that higher than your maxhp, this counter doesn't work.
-if you use 2 or 3 equipment with counter effect on it stats for example you use d.mail with ensis shield, when monster deal 5k damage on you and counter from both equipments are triggered, you will get 10k hp, in other words you can do self healing without using skills or hp pot.
-this counter effect will be lost if you put any crysta that consume autoskill on it, ifrit for example (I'm not really sure about this one since i never put ifrit/cherose/dajarte or any similar crysta that consume auto skill on those equipments)

You can see my video on youtube, enchanter vs parazaia. I used d.mail with ensis shield on that video. You can see there if the counter from those equipment are triggered, my mp will get healed eventho i didn't cast mp heal on my self or using remagic and at the same time my hp still stayed the same or also got healed, since enchanter has passive skill that can convert a bit portion of monster damage to mp.