Trim size 4 × 6 in (standard postcard)
Bleed 0.125 in all sides — total artboard 4.25 × 6.25 in
Safe area 0.125 in inside trim
Colors are sRGB — ask your printer for a CMYK proof if exact brand-color matching matters.
Before printing/exporting: in the print dialog, set Scale to "100" / "Actual size" — NOT "Fit to page." "Fit to page" is what shrinks this to ~94% and throws off the exact 4×6 in trim size.
Trim line
Safe area
Card edge = bleed edge