承 浮 函 These look a bit alike, even have similar meanings, sort of. All are second tone.

承 cheng 3 hands (on the sides) lifting a person (in the middle) = to receive [My parents, when I am a baby]

浮　fu a child floating in the water suspended by an adults hand. child on the bottom right, hand on top right, water on the left side. Floating (in water) [My dad teaching me to swim]

函　han arrow case i.e. a quiver. Idea is: Containing, Carrying (a box of arrows). Envelope, case, letter.  

一封信　yi1 feng1 xin4  = a letter