Anytime an image or PDF is attached to an email in the OS X Mail app, you will be presented with a preview of that picture or document. Likewise, if someone emails you photos those images are then drawn on screen within that email as previews. While this is a great feature for most of us, drawing those inline graphics can be a very sluggish experience on older Macs with less system resources, and with the help of a defaults command you can turn off those image previews and speed up performance of Mail.app quite a bit.
Disabling Image Attachment Previews in OS X Mail
- Quit Mail app
- Launch Terminal, found within Launchpad or /Applications/Utilities/ and enter the following command string:
defaults write com.apple.mail DisableInlineAttachmentViewing 1- Relaunch Mail for changes to take effect
Update: some users have reported issues with the original defaults command, try this variation if it did not work for you (Thanks Ken & Elwira!):
defaults write com.apple.mail DisableInlineAttachmentViewing -bool true
Opening an email message with image attachments will now simply show a general thumbnail showing the file type, along with the file name, as if it was in the Finder.
You can double-click those icons or thumbnails to open the image in Preview, or you can use drag and drop to save the picture somewhere to the file system or on the desktop.
Performance Increase Limited to Macs with Less Resources
Though this shouldn’t be necessary for most users for speed purposes, it undoubtedly makes a difference on Macs that have fewer resources available. For example, we tested having the image previews disabled on an older base model MacBook Air (2010) with 2GB of RAM and a 1.4GHz Core 2 Duo processor, and it made a significant difference in the performance of the Mail application when sending and receiving multiple large full resolution photos to and from an iPhone, particularly when Mail app was open concurrently with several other applications. The reason is fairly simple, Mail no longer has to draw image previews and resize each of the graphics to display on screen, thus using less RAM and requiring less processor utilization to simply send and receive those messages.
The speed improvements will probably be even more pronounced on older Macs with less resources, or older Macs that are frequently in more demanding situations. In testing, the difference can be profound enough that I would add it to the list of things to do when trying to speed up the performance of older Macs, especially for anyone who has complaints about the performance of Mail itself.
It should be mentioned there was virtually no performance difference offered for Mail app running on a newer model MacBook Air or MacBook Pro, but those machines have plenty of hardware to handle redrawing 8MP photos on the fly, whether its in the Mail application or elsewhere. It might be easiest to say this: if your Mac feels sluggish and slow when managing pictures, documents, photos, or any other kind of attachment in the OS X Mail app, then try this tip out. If you have no complaints, don’t bother because it’s likely not necessary.
Show Image Previews in Mail Again (Default)
To revert back to the Mail default behavior:
- Quit Mail, then launch Terminal again and enter the following defaults command:
defaults write com.apple.mail DisableInlineAttachmentViewing 0- Relaunch Mail to be back to the default image previews
Update: some users reported issues with the original defaults command, try this if you are having problems:
defaults write com.apple.mail DisableInlineAttachmentViewing -bool false
The same email as above is again shown, this time with the image preview drawn in the message window as the default setting:
Heads up to MacWorld for basis of this tip idea by pointing out a similar defaults command.
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