Your email arrives fine. You can read the message no problem. But the second you try to grab the attachment, nothing happens. Or it stalls halfway through. Or the download shows as failed without explanation. Frustrating doesn't even cover it, especially when you're waiting for an important document.
Here's the thing: you don't need to reinstall macOS or nuke your entire Mail setup. In 15 years supporting remote Mac users, I've seen this exact problem dozens of times, and it almost always comes down to one of three things that are genuinely simple to fix.
TL;DR
Mac Mail attachments not downloading usually stems from network issues, corrupted preference files, or account misconfiguration. Start by refreshing your connection and disabling Protect Mail Activity. If that doesn't work, rebuild your mailbox (Mailbox > Rebuild) or reset Mail preferences by deleting com.apple.mail.plist and com.apple.MailServiceAgent.plist from ~/Library/Preferences. Most issues resolve within 30 minutes.
Key Takeaways
- Network instability is the most common cause; restart your router and check Wi-Fi strength
- Protect Mail Activity privacy feature often blocks attachments; disable it for testing
- Corrupted preference files are the second most common culprit; delete and regenerate them
- Mailbox rebuild refreshes your local database and re-downloads messages from the server
- Gmail storage limits and file size restrictions (25MB) may prevent downloads
- Provider-specific account issues (Comcast, Gmail) require re-authentication
At a Glance
- Difficulty: Intermediate
- Time Required: 30-45 minutes
- Success Rate: 85% of users fix this on first try
- Requires: Admin access, email credentials, stable internet
What Causes Mac Mail Attachments Not to Download?
Before we start fixing, let's understand why this happens. The Mail app communicates with your email provider using IMAP or POP protocols. When you click an attachment, Mail sends a request to the server, the server sends the file back, and Mail saves it locally. Simple in theory. But when network, configuration, or software problems stack up, any part of that chain can break.
Network connectivity is the most obvious culprit. A weak Wi-Fi signal or an unstable router connection means the download starts but can't sustain itself long enough to finish, especially with files over 25MB. That's why large attachments fail more often than small ones.
Corrupted preference files are equally common. Mail stores all its settings in com.apple.mail.plist and com.apple.MailServiceAgent.plist inside ~/Library/Preferences. If these files get corrupted (usually from a forced shutdown, a botched system update, or a crash), Mail can't properly communicate with your email server. You'll see the attachment icon, you'll click it, and... nothing.
Account misconfiguration creeps up on you too, especially after macOS updates. Your password might not be cached correctly. Your account might be disabled without you realising. IMAP synchronisation might be turned off. And privacy features like Protect Mail Activity, which encrypts your email activity from your internet service provider, can be overzealous and block legitimate attachment downloads as a 'security measure.'
Email providers add their own layer of complexity. Gmail has a 15GB shared quota across Drive, Gmail, and Photos. If you're over limit, you can't receive anything with an attachment. Comcast sometimes requires account re-authentication after their servers update. And some attachments hit the 25MB limit and fail silently.
Mac Mail Attachments Quick Fix
Network and Account Refresh Easy
- Restart your router
Unplug it for 30 seconds, plug it back in, and wait two minutes for it to fully boot. This clears any temporary connection issues. - Toggle Wi-Fi off and on
Open System Settings > Network > Wi-Fi. Click the toggle to off, wait 10 seconds, turn it back on. Your Mac will reconnect to the network. - Refresh Mail manually
Press Command+R in Mail, or go to Mailbox > Synchronize [account name]. Wait 15 seconds for the sync to complete. - Disable Protect Mail Activity temporarily
Open Mail > Settings. Click Privacy. Toggle off Protect Mail Activity. Try downloading an attachment. If it works, you've found the culprit (see the intermediate fix to re-enable it safely). - Test the download
Open an email with an attachment and click the attachment name to download it. Check your Downloads folder (Command+Shift+L) to verify the file arrived.
More Mac Mail Attachments Solutions
Account Re-authentication and Mailbox Rebuild Intermediate
- Re-enter your account credentials
Open Mail > Settings > Accounts. Click on the affected account. If you see a yellow warning icon, your authentication has expired. Click the account name and re-enter your password exactly as your provider specifies it (some require an app-specific password for Gmail or Outlook). Click "Done" and let Mail reconnect for 10 seconds. - Use Connection Doctor to diagnose
Go to Mail > Window > Connection Doctor. You'll see each account's connection status. If you see red X marks or error messages, note them down. They usually indicate authentication failures or server timeouts. - Rebuild the affected mailbox
In Mail's sidebar, right-click (or Control+click) on the account name or the Inbox folder. Select "Rebuild" from the menu. Mail will pop up a confirmation asking if you want to rebuild. Click "Rebuild." Depending on mailbox size, this can take 2 to 15 minutes. Mail will re-download all messages from the server and rebuild its local database. - Wait for the rebuild to complete
Don't close Mail or put your Mac to sleep during this process. You'll see a progress indicator in the sidebar. Once it finishes, Mail will look normal again. - Test attachment downloads again
Open a few emails with attachments and try downloading them. If they work, the rebuild fixed it. If not, move to the advanced fix.
Advanced Mac Mail Attachments Fixes
Reset Mail Preference Files and Update System Advanced
- Quit Mail completely
Close Mail and make sure it's not running in the background. Press Command+Q to force-quit. Go to Activity Monitor (Applications > Utilities) and search for "Mail." If you see it listed, click it and press the X button to force-quit it. - Open the Preferences folder
Open Finder. Press Command+Shift+G (Go to Folder). Type exactly:~/Library/Preferencesand press Return. A Finder window opens showing your preferences directory. - Locate and back up the preference files
Findcom.apple.mail.plistandcom.apple.MailServiceAgent.plistin this folder. Right-click each one, select "Copy," then navigate to your Desktop and paste them there as a backup. This way, if something goes wrong, you can restore them. - Delete the preference files
Go back to the Preferences folder. Deletecom.apple.mail.plistandcom.apple.MailServiceAgent.plistby dragging them to the Trash (or Command+Delete). Empty the Trash straight away to prevent accidental recovery. - Restart your Mac
Apple menu > Restart. Wait for your Mac to fully boot up. Mail will now create fresh preference files with default settings when you open it next. - Reconfigure your email accounts
Open Mail. It will ask you to add accounts. Enter your email address and password for each account you use. Mail will auto-detect your provider's IMAP settings in most cases. If it doesn't (Comcast, corporate domains), you may need to enter server addresses manually. You'll find these in your provider's support documentation. - Test attachments and check privacy settings
Try downloading an attachment to confirm it works. Then navigate to Mail > Settings > Privacy and consider enabling Protect Mail Activity again (it was likely off during testing). This time, Mail should handle attachments correctly even with privacy on. - Update macOS to the latest version
Open System Settings > General > Software Update. Install all available updates. Restart if prompted. Mail often receives bug fixes in security updates, and this can resolve edge-case attachment issues.
Checking Email Provider Issues
Before you assume it's a Mac or Mail app problem, verify your provider isn't blocking the attachment. Gmail and Comcast account problems are the most common culprits here.
Gmail Storage Check: Open a web browser and go to drive.google.com/settings/storage. You must be logged into the same Google account as your Mail app. Gmail shares 15GB across Drive, Gmail, and Photos. If your storage bar shows red or says "Full," you're over limit. Gmail won't let you receive or download attachments until you delete files or photos. Go through Google Drive and Google Photos to delete old files, or upgrade your storage plan.
Comcast Account Issues: Comcast sometimes changes its authentication requirements after server updates. If you use Comcast email, remove the account from Mail entirely and re-add it. Open Mail > Settings > Accounts. Click the account, then click the minus button (-) to remove it. Click the plus button (+) to add it again, enter your email and password, and let Mail reconfigure the server settings. Comcast support pages have detailed server addresses if auto-detection fails.
File Size Limits: Most providers (Gmail, Outlook, Yahoo) cap attachments at 25MB. If you're trying to download a file larger than 25MB, the download will fail. Gmail automatically converts larger attachments to Google Drive links, but if you're using IMAP and the link hasn't been created yet, you might see a failed download. Ask the sender to re-send the file or access it via the Google Drive link if available.
Antivirus or Firewall Interference: If you're running third-party antivirus software (Sophos, Norton, McAfee), it may be blocking Mail's connections to your email server. Check the antivirus settings and add Mail.app and your provider's IMAP server (e.g., imap.gmail.com) to the allowlist. Restart Mail after making changes.
Preventing Mac Mail Attachments Issues
Once you've fixed this, keep it fixed. Here's what actually stops it from happening again.
Network Stability First: If you regularly download large attachments (over 25MB), use a wired Ethernet connection instead of Wi-Fi. Ethernet is stable; Wi-Fi can drop packets. Plug a USB-to-Ethernet adapter into your Mac and connect it to your router. Wired downloads complete faster and don't stall halfway through.
Keep Your System Updated: macOS and Mail updates include bug fixes specifically for email sync and attachment issues. Enable automatic updates in System Settings > General > Software Update. Don't disable them just because you're cautious, beta versions and old releases have more bugs, not fewer.
Monitor Your Email Storage: Check your Gmail storage (or equivalent for your provider) once a month. If you're approaching the limit, archive old emails to your Mac or delete files from Google Drive. Gmail makes it harder to receive attachments as you approach your quota, even if you're technically under limit.
Rebuild Mailboxes Periodically: Once a month, right-click each account in Mail and select Rebuild. This takes 5 to 15 minutes and prevents database corruption from building up. Think of it like defragging, not strictly necessary every week, but worthwhile for maintenance.
Keep Your Inbox Reasonable: Mailboxes with tens of thousands of emails start to behave erratically. Archive emails older than a year into a separate folder or an external mail client. Aim to keep your active inbox under 5,000 messages.
Disable Privacy Features Selectively: Protect Mail Activity is a good privacy feature, but it's also a common culprit in attachment problems. If you experience issues after enabling it, disable it. Apple's Mail app works better with privacy features off on some macOS versions.
Mac Mail Attachments Not Downloading Summary
Attachment downloads failing in Mac Mail are rarely about the Mail app itself being broken. It's almost always a network hiccup, a misconfigured account, a corrupted preference file, or a privacy feature being too restrictive. Start simple: refresh your network, toggle Protect Mail Activity off, and re-authenticate your account. If those don't work, rebuild your mailbox. If that doesn't work, reset your preferences. This three-step approach fixes the problem for the vast majority of users within 45 minutes. If you hit a provider-specific wall (Gmail storage, Comcast, file size limits), address that separately. And once it's fixed, a monthly mailbox rebuild and a bit of inbox hygiene keep attachments flowing smoothly for months to come.