Have you ever noticed that Mail’s alert sounds are quite low? Even in my home office, if iTunes is playing I often won’t even hear the new Mail alert sound—and that’s with the Alert volume slider (in the Sound System Preferences panel) set to its loudest setting. The problem is that the pre-recorded Mail alert sounds are simply too quiet for most typical environments.
You can fix this yourself, though it will take a bit of work with an audio editor. Luckily, there are many such programs out there, including the freeware Audacity. The following instructions assume you’ll be using Audacity to do the editing; if you use another program, the specifics of editing the sound file may differ slightly, but the general process will be the same. Here’s what you need to do.
Download and install Audacity (grab version 1.2.4b), then launch it and leave it running. If you’re using an Intel Mac, follow the link on the download page for an experimental Intel-compatible release. I haven’t tested that version of the program, but it should work fine for this simple edit. Next, quit Mail if it’s running.
In the Finder, Control-Click on Mail (in /Applications) and choose Show Package Contents from the pop-up menu. In the new window that opens, navigate into Contents -> Resources; this is where the sound files reside. We’ll be modifying four sound files—Mail Fetch Error.aiff, Mail Sent.aiff, New Mail.aiff and No Mail.aiff—so the first thing to do is to back these up. Do that by holding down the Option key (to force a copy) and dragging them to another spot on your hard drive.
Now drag and drop one of the sounds onto Audacity’s icon in the dock; I’ll use No Mail.aiff for this how-to, but the steps are the same for each of the sounds. (Leave the Resources window open, as you’ll be using it later.) You should now see something like this:

That’s the main Audacity window, showing the left and right channels for the No Mail.aiff sound file.
If you want to hear the alert sound, just click the green Play triangle in the top portion of Audacity’s window. Notice how quiet it is, especially compared to your iTunes or system alerts. That’s what we’re going to fix. To the left of the channel display are a couple of buttons (Mute, Solo) and two sliders. The topmost slider controls the gain, or amplification, of the sound. That’s what we’ll use to increase the volume of the alert sound.
Here’s where things get a bit odd, as you can’t just select File -> Save—mainly because Audacity has no such menu option! Instead, you need to export the sound, but only after choosing an export format. Open Audacity’s Preferences, and click on the File Formats tab. In the Uncompressed Export Format section, set the pop-up to AIFF (Apple/SGI 16 bit PCM), then click OK. Now choose File -> Export as AIFF, and save the file to your Desktop.
Switch back to the Finder, and drag your newly-modified sound file back into the Resources folder—click
yeswhen the Finder asks if it’s OK to overwrite the file that’s already there (as you’ve already backed up that file elsewhere, right?!). Repeat this process for each of the three other sounds, then launch Mail. You should find that your Mail alerts are now much more audible above the background noise of your work environment.
Note that when you’re done, you may wish to run Disk Utility’s Repair Permissions routine, as editing files in this manner changes their ownership. If you ever want to revert your changes, just replace the modified files with the originals you backed up before you began, and then run Repair Permissions again. (Nothing will actually break if you don’t repair permissions, but I try to leave permissions intact whenever possible.)