Gmail – Reject an email addressed to too many recipients in Gmail

There are currently 3 basic ways to reject unwanted messages in gmail:

1. Mark as Spam

   Unlike your belief, you can safely mark anything you consider slightly annoying or unrequested as a spam. And you should do it. I've marked mails directly from my primary contacts as spam, and never lost any important mail because of that. Just to illustrate to your specific case, gmail even offers an automatic unsubscribe feature for some lists if you click on Mark as spam. Should the worst happen and you find legitimate messages on the spam folder, there are fixes for that, such as adding their e-mail to your contacts or using filters.

2. Filter

   If you can come up with a simple enough rule that will work for your sample, you can safely create a filter. If you have any doubts, instead of throwing stuff to trash, set a label and archive the message, so you can review the filter later on. Simple stuff.

3. Priority Inbox

   That's even more magical. In my case, it was almost useless because I've been using the first two features and activating it didn't help much. But it's great nevertheless. Just set it up, try it and see if it's a fit. The whole idea behind it is exactly what you've requested: reject unwanted messages that you don't want to send to spam or trash. Maybe it's a mail list you subscribed yourself. You can rank it as unimportant, if gmail didn't already did it, and it will stay on your inbox for further review.

Your best bet is probably to download them via IMAP and use a mail client's more powerful search capabilities if you value your time.

If you're intent on using the browser, in Gmail settings, turn on personal level indicators and set your maximum page size to 100 conversations/page. Then do a search for 'cc:me OR to:me'. Then do a find in page for the character › (which will highlight messages that are sent to you+others. This might take a while, but is way quicker than sorting through them all.