Google's Gmail Web-based email service runs on the Internet Message Access Protocol system, but it also offers Post Office Protocol mail server access.
Definition of LUMEN. 1. 2. : the bore of a tube (as of a hollow needle or catheter). 3. : a unit of luminous flux equal to the light emitted in a unit solid angle by a uniform point source of one candle intensity.
The definition of a lumen in biology is the inside space of a tubular structure such as an artery or an intestine. A lumen can also be the inside space of a cellular structure duh as the endoplasmic reticulum.