I was attacked in this way a couple of months back. I use a different email address for each account (of the pattern product@example.com), and use a separate address for Git commits (like git@example.com). It was this second one that was attacked and I ended up with some 500 emails within 12 hours. Fortunately, since I don't expect anyone to actually email me on the Git address, I just put up a filter to send them all to a separate folder to go over at my leisure.

After 12 hours, the pace of emails came to a halt, and then I started receiving emails to made up addresses of a American political nature on the same domain (I have wildcard alias enabled), suggesting that someone was perhaps trying to vent some frustration. This only lasted for about half an hour before the attacker seems to have given up and stopped.

Strangely, I didn't receive any email during the attack which the attacker might have been trying to hide. Which has left me confused at to the purpose of this attack in the first place.

I had this happen recently too, also not covering up any email activity (I combed through 3000+ spam emails).

Double check that there are no forwarding rules added to your inbox and add some protection against a SIM swap.

In my case, they didn't compromise any of my accounts but did attempt to open a new credit card so it would be worth double checking your credit reports.