I would probably assign "select(1, _G["MailFrame"]:GetRegions())" to a variable so you don't have to keep calling that. I think you only need
local icon = MailFrame:GetRegions().
Lua Code:
local icon = MailFrame:GetRegions()
local frame = CreateFrame("Frame", nil, MailFrame)
frame:SetPoint("TOPLEFT", icon, 1, -1)
frame:SetSize(55, 55)
frame:SetFrameStrata("HIGH")
CreateBorderLight(frame, AftermathhUI.media.bordersize, AftermathhUI.bordercolor, AftermathhUI.bordercolor, AftermathhUI.bordercolor,0)
icon:SetSize(55, 55)
icon:SetPoint("TOPLEFT", 16, -14)
icon:SetParent(frame) -- Since its hidden already we need a new parent.