I am no designer, or I would submit my own ramblings is design form. So a measly 0.02 DRK if you'd permit.
Darkcoin/Darksend, as a name is beautiful. BUT... associated with the notion of "sending money anon" has two implications. Illegality vs freedom.
Rainbows make it look like "gay freedom" and 1985 design. Dark blue and black make it look Darth Vader'ish and too obscure. The envelope makes it look like a Gmail app (and IMHO is horrible as an independent symbol of DRK, and implies representation of locked email because of gmail graphic association)
Think of something positive, associate it with freedom. Don't make it look gay. Dark blue/black looks cool as f*ck IMHO, but the edges in the arrows seem too authoritative. I would keep the dark/blue/arrows, but introduce some fluid curves around the actual logo and 2 arrows, pointing opposite direction, around the DRK logo, meaning DRK makes is anonymous, but the two-way direction-flow makes it feel "easy to come and go"
Like the snakes in the pharma symbol, sort of. To represent easy of use, fluidness, organic of sorts, DRK as center, opposite direction pointing arrows meaning - two way connecting communication.