User on Office 365 for email, gets spammed with 7000+ emails – the usual porn, drugs stuff.  Most went into the Junk folder. User deletes them all, then after approx. 4+ days we get requested to investigate what happened. When checking the Office 365 admin control panel and the incoming email stats, theres no sign of those 7000 emails ever hitting Office 365.  User does not have multiple accounts or anything setup, just the single O365 email account.

I tried a recover deleted items, and only found a single spammy email.

So where the hell did these emails come from, and/or why did O365 not see them in its stats as incoming email ? Any ideas or things to check ? Users systems have been checked over and virus/malware free.