Click the Storage tab and then select Manage -> click on Mail in the left-hand sidebar. Click on the “Apple menu” and select About this Mac. With the latest macOS, you can also use the optimize feature to delete attachments.This will sort out all messages with attachments.
If you are having trouble finding emails with attachment, simply click the View menu, and then select View by attachments. Alternatively, you can simply delete the email, and proceed to your download directory in the library on your Mac to delete downloaded attachments. To delete, simply navigate to messages with attachments, click Menu and select Remove attachment. Here is a step-by-step guide on how to delete mail storage on Mac. Once you open an attachment on your Mac, it automatically gets downloaded on your computer. These attachments range from sent documents and other files to signatures from subscribed company newsletters. Mail storage is consumed by various attachments that come with your emails.