There is much speculation here. But to be honest, this appears to be an isolated incident that has some plausible explanations. I work in an exclusive Google/gmail environment, and have used gmail since it was launched back in 2004 with no problems at all.
We don’t know the details, such as:
– non-gmail accounts (he mentioned AOL) being forwarded to his gmail account. There are many configurations that are possible that would cause this to happen that would only be related to gmail because gmail is being used as bucket to accumulate mail from other services.
– We don’t know if he archives or deletes his mail or both. If the concern is that a bunch of archived email now appears in the inbox, this would be possible if someone had access to his pc, and could be done with 3 clicks.
– We don’t know if he uses a weak password or has been hacked. If someone gets into your email, they can do all kinds of crazy things.
– We don’t know if he had ever used a mail client with gmail (outlook, thunderbird, etc). Related to this, we don’t know how this was configured (IMAP, etc). Using mail clients can be a great way to screw up your email.
– We don’t know if he had ever used one of the gmail data retrieval apps. These are notorious for screwing up data. And if the app is still on a pc, it could still be doing damage.
Check out the gmail’s known issues and contact google if you have exhausted the other possibilities.