Hi edatsy,
Thanks for posting in Apple Support Communities. It sounds like you've taken some great steps so far.
If you have more than one email account on your Mac, it might help to isolate which accounts are individually using more storage. The following is from View email account information in Mail on Mac.
1. In the Mail app 
on your Mac, in the Mail sidebar, Control-click a mailbox, then choose Get Account Info.
2. In the Account Info window, click the Account pop-up menu, then choose an account.
3. Click a tab to view details about the account.
• Quota Limits or Messages on Server: Monitor the size of mailboxes and messages on the mail server. This information can help you manage your messages when you exceed your account storage limits. For example, for an IMAP account, you can determine which mailbox uses the most space, show the messages, then delete them.
• Summary: View a summary of account settings, such as those related to mail servers and security.
Also, you mentioned delete settings. If you haven't already, take these steps from Free up storage space for email accounts in Mail on Mac including emptying your Trash mailbox.
In the Mail app on your Mac, do any of the following:
• Delete large messages or messages with attachments, or move the messages to a mailbox on your Mac.
Tip: To quickly identify large messages, choose View > Sort By, then choose Size.
• Delete attachments that you saved. Choose Message > Remove Attachments; the message remains in the mailbox and Mail indicates attachments were manually removed.
For IMAP accounts, be sure to download the attachments first—attachments are deleted from the mail server and can’t be retrieved.
• Empty your Trash mailbox. Messages you recently deleted are in the Trash mailbox but haven’t yet been removed from the mail server. Choose Mailbox > Erase Deleted Items, then choose to remove them from all accounts or a specific account.
• For POP accounts, reduce the amount of time that copies of messages and attachments remain on the mail server before being removed. Choose Mail > Settings, click Accounts, select the account, click Advanced, then choose a different option from the pop-up menu below “Remove copy from server after retrieving a message.”
All the best.
