TidyMacYes. ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads holds copies of attachments you opened from Apple Mail. The originals stay in your emails, so removing these copies loses nothing; opening an attachment again simply makes a new copy.
The five questions
Copies of attachments you opened from Apple Mail.
Every attachment you open is saved here and kept.
Yes. The original stays in the email.
Opening an attachment again simply makes a new copy.
Yes, as you open attachments.
How big it gets: 0.5–10 GB, depending on how many attachments you open.
Where it lives: ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads
Do it yourself
In Finder choose Go > Go to Folder, type ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads, and move its contents to the Trash.
open ~/Library/Containers/com.apple.mail/Data/Library/Mail\ Downloads
See your own mail attachment copies in seconds
Scan free, see every part of your storage explained, and clean only what’s safe. Everything goes to the Trash first.
Frequently asked questions
Is it safe to delete mail attachment copies on a Mac?
Yes. The original stays in the email.
Why are my mail attachment copies so big?
Every attachment you open is saved here and kept.
What happens after I remove mail attachment copies?
Opening an attachment again simply makes a new copy.
Will mail attachment copies come back?
Yes, as you open attachments.
How do I clean mail attachment copies manually?
In Finder choose Go > Go to Folder, type ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads, and move its contents to the Trash.