In Gmail, is there a query I can use to find all emails before a certain date? My company currently has a mailbox with 500K emails and it's starting to get really slow when performing a query. I'd like to start keeping it pruned to only the last 6 months worth of e-mail.
Yes, use Gmail advanced search operators, for instance:
For Gmail users
Step 1: Type "older_than:Xy" into search (X being the value in years that you want to highlight and eventually delete. You can also do months or days by using m or d instead of y)
Step 2: Hit the select all button in the upper left hand of the inbox
Step 3: When all of the entries on that page are highlighted, a line that says "All 50 conversations on this page are selected. Select all conversations that match this search" should come up at the top of the inbox. Click on that. This will select all of the emails that matched your search criteria (that is, everything older than so many years)
Step 4: Hit delete.
Before:[date] is the query you're looking for, here's where I found the answer: https://support.google.com/mail/answer/7190?hl=en