The OS X Firewall provides an optional ability to block all incoming network connections, offering a significant security boost to Macs that are located in untrusted networks or hostile network environments.

Because this is the strictest level of preventative network access possible in OS X through the built-in Mac firewall, the ideal usage is for situations where the default assumption would be to not trust any incoming network connection attempts. Accordingly, this is simply too strict to be practical for average users in most environments, but it is at least worthwhile knowing how to enable the feature should it become necessary at some point.

Blocking All Inbound Network Connections in OS X

This feature is available in all versions of Mac OS X:

• Open System Preferences from the  Apple menu and choose the “Security & Privacy” panel


• Select the “Firewall” tab and then click the lock icon in the corner to login and allow changes


• Choose “Turn On Firewall” if it hasn’t been enabled yet, then choose “Firewall Options”


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• Select the topmost “Block all incoming connections” option

As noted by the preference panel, when enabled this blocks all network connections to the Mac, including all sharing services, all file sharing through networks, screen sharing, remote access, remote login, and remote connectivity through SSH and SFTP, iChat Bonjour, AirDrop file transfers, iTunes music sharing, ICMP requests and responses – literally everything that is inbound which is not required for basic internet connectivity and servicing.

Blocks Inbound Connections, Not Broadcasts

It’s important to note this setting will not prevent the Mac from broadcasting it’s presence on a network if certain networking features are enabled (like File Sharing, AirDrop, Samba for Windows sharing, etc) and it does nothing to prevent outgoing connections, it will only impact inbound connection attempts from all nonessential internet services. For a specific example; if a user left File Sharing turned ON but blocked all incoming connections with the firewall, the Mac would still show up on network scans, but nobody would be able to connect to it. If blocking the Mac from broadcasting it’s presence on a network is desired as well, simply go to the “Sharing” preference panel and turn off the services that are revealing it’s presence.

Removing attachments from an email or everything in Mail app can be useful for a variety of reasons, from ditching a file that is no longer relevant to an email thread, to lowering the file transfer size when sending/replying to a message, or for more extreme cases for individuals with smaller hard drives, for reducing the overall disk space consumed by the Mail attachments directory.

Whatever the case, use some caution when removing attachments this way, as there is no way to retrieve the mail attachment locally after they have been removed from Mail app. For this reason, if you intend on deleting many attachments from many emails you may want to make a manual backup of the attachment directory beforehand, which we will also cover below by showing you where the attachment files are stored in OS X.

Remove Attachments from a Single Email in OS X Mail

To ditch attachments for a single mail message:

• From the Mail inbox, either select the email message to remove the attachment from, or open the email directly


• Go to the Messages window and choose “Remove Attachments”

Any email with the attachment removed this way will now show the following message in place of the attachment itself:

[The attachment filename.jpeg has been manually removed]

If you have Mail image previews turned off, a tiny 1kb text file called “Mail Attachment” will be bundled with the message instead, which contains the same message.

Bulk Removing Attachments from Multiple Email Messages in Mail App

This is not necessarily recommended unless you take the time to backup all of the attachments first, otherwise you may permanently lose access to the attached files.

• From the primary Mail app inbox, hit Command+A to select all


• Pull down the Messages menu and choose “Remove Attachments”

You can repeat the process for drafts, sent folder, and Trash if necessary.

Based on repeated experience, it can be a good idea to rebuild the mailbox after mass deleting attachments to prevent any peculiarities with Mail app.

Mail Attachments Location in Mac OS X for Manual Backups

Mail data and attachments are backed up automatically by Time Machine, but if you’re going to delete them all from the Mail app you may want to manually back them up first. Typically, all Mail attachments are stored in the following directory:

~/Library/Mail/V2/

You can manually back up this entire directory if necessary by copying it over to an external drive or elsewhere on the Mac.

Backing up the entire directory will grab everything for your Mail app inboxes and all mail accounts. If you’d prefer to be more specific, you’ll find that opening the V2 directory will reveal the name(s) of email accounts setup to use with Mail app, and buried within those directories in a somewhat confusing maze of files is the attachment data, typically in a subdirectory like this:

IMAP-email@address/INBOX.mbox/21489C-1481F-812A-B2814/Data/Attachments/

Within that Attachments subdirectory will be even more subdirectories, labeled randomly as numbers, containing additional subdirectories with the attachment files themselves. Yes, the directory structure seems unnecessarily complicated.

Here’s an example Finder window with an attachments folder opened in hierarchy view:

Because of the complex directory structure, it’s often easiest to just copy or backup the entire ~/Library/Mail/V2/ directory rather than looking around for individual files. Going that route also makes it easier to restore the attachments to Mail app, because all that is required is dragging/copying the entire V2 directory back into the ~/Library/Mail/ directory.

Whether or not it’s necessary to backup and delete the Mail attachments folder is ultimately up to you, but if you find that it’s taking up a lot of disk space by scanning a drive with an app like OmniDiskSweeper, it may be a worthwhile endeavor for those with very limited disk space.