Gmail doesn’t offer a way to search and sort email messages by size but you can use a tool like Microsoft Outlook or IMAP Size to sort your mails by the size criteria on the desktop. They connect to your Gmail account via IMAP and therefore when you delete an emails with big attachments locally, the same happens in your online inbox as well.
If you however find the above workarounds a little complicated, there’s an even simpler method now that won’t even require you download or install anything – it’s called findbigmail.com.
It will quickly find all the big email messages in your Gmail account that are taking up the maximum space. These messages are categorized with special labels like “Big Mail” or “Really Big Mail” to help you decide which of them should be removed to recover more space.
To get started, you simply connect your Gmail account with Find Big Mail using Google’s OAuth. It then scans all your messages for their sizes and send you an email notification once the scan is over (I got mine in about 8 minutes).
You can then log into your Gmail account and act on messages marked as “Big Mails” to instantly reclaim space.