My friend has a flight from Lima (LIM) to London (LHR) via Mexico City (MEX), all on one ticket with Aeromexico.
I understand that Mexico, like the US, doesn't do sterile transit, so he'll have to pass Mexican immigration.
Will he also need to collect and re-check his checked bag, like in the US, or will it be loaded directly onto the second flight (like when transiting pretty much anywhere else)?