I have over 50,000 emails. How can I make the Mail app go faster?
I would start by deleting the account and then recreating it.  However, before you do, make sure you set the "Download Attachments" option in the Account Settings

You have three options:


All - automatically downloads all attachments
Recent - mail from the past 15 months.
None - you have to manually download attachments.


So, as you're recreating your GMail account, select "Recent" or "None."  Then, as it synchronizes with your email account, it will only download the attachments that fit those rules.