From Ender in Exile (the only sequel I have to hand), Ender gets a different email address on practically every email:
GovNom%Colony1@colmin.govGovDes%ShakespeareCol@ColMin.gov/voyGov%ShakespeareCol@ColMin.govAWiggin%Ganges@ColLeague.admAWiggin%Ganges@ColLeague.Adm/voyEWiggin%Ganges@ColLeague.Adm/voy
From the above, one might guess that the part after the slash gets amended to indicate which mail relay to pass through (ships presumably would have their own relay to handle the difficulties of faster-than-light communication). However, Valentine gets:
vwiggin%Colony1@colmin.gov/citizen(while on the same ship as Ender who has/voyat the time)- followed shortly thereafter by
vwiggin%ShakespeareCol@ColMin.gov/voy==PoslDreq(the only instance of==) - and finally,
vwiggin%ShakespeareCol@colmin.gov/voy, matching Ender's official email.
As seen above, MinCol (later ColLeague) seems to use the %-part to indicate which colony a person belongs to. Meanwhile, IFCom apparently uses it for the person's rank:
qmorgan%rearadmiral@ifcom.gov/fleetcomchamrajnagar%polemarch@ifcom.gov/centcomimo%testadmin@colmin.gov
heg.gov seems to follow this convention as well, though hegemony.gov uses the /-part for that:
hgraff%mincol@heg.govPeterWiggin@hegemony.gov/hegemon
What explains this proliferation of email formats, and apparent fluidity of addresses? The %-part is partially explained by early email gateways (for example ColMin might be using them this way, though it seems like a subdomain would be better), but that doesn't explain all of the uses and I can't find any precedent at all for the /-part.