We have analyzed the transmission process through single subwavelength apertures surrounded by a set of periodic grooves in optically thick Ag films. On one hand, we found that the intensity of both single- and double-corrugated structures follows just one exponential regime as a function of the hole depth. On the other hand, it is shown that the transmission process can be separated into three independent steps: coupling in, transmission through the aperture and coupling out. This is in contrast with the transmission through hole arrays reported by previous studies where two transmission regimes were found. These findings are of relevance not only for further understanding the enhanced transmission but also for any applications based on this phenomenon.