Gmail attachment won't upload or stuck at 0%? Why 'Attachment failed' happens, and the fix

Start here: read the message, then run a 30-second test

Attach a very small file, such as a one-page document, to a new email. If it uploads, your account and connection are basically working, and the size of the original file is the first suspect. If the small file stalls as well, skip to storage, connection and browser. Then match what you see:

• Stuck at 0% or uploading forever: we could not find this explained as a specific error in Google's help. Work through storage, connection and browser below.
• 'Attachment failed': we could not find this wording explained in Google's Gmail help pages. Treat it as a general upload failure, remove the file and add it again, then go through the causes below.
• 'Couldn't send message': Google says one or more files didn't upload to Drive, and that this might be because you don't have enough space, your internet is slow, or something else. To send the message, remove or re-add the attachment.
• 'Gmail's adding files': you started uploading from another device. Wait until that upload completes, or remove the attachments that are still uploading if you need to send right away.
• A message saying the file was blocked for security reasons: this is a file type rule, not an upload fault. Gmail doesn't let you attach executable files such as .exe, and our separate guide to blocked attachments covers it.

Cause 1: The file is over the limit, and the Drive link is the way through

For personal Gmail accounts, the limit is 25 MB. It applies to the total attachment size, so five 6 MB files will go over it just as one 30 MB file will. Work and school accounts follow whatever limit the Google Workspace administrator has set.

Google says that if your total attachment size is greater than the limit, Gmail automatically removes the attachment and adds it as a Google Drive link in the email. So a large file is now uploading to Drive rather than to the message itself, and any problem with Drive storage or your connection will stop it. If the compose window keeps stalling, upload the file at drive.google.com first, then insert it. To send a file that is already in Drive:

• Open Gmail on your computer and click 'Compose'.
• At the bottom of the message, click 'Insert files using Drive'.
• Select the file. At the bottom of the page, choose 'Drive link', then click 'Insert'.
• When you send, Gmail prompts you if a recipient doesn't have access. Choosing 'Anyone with the link' means recipients don't need a Google Account, but anyone holding the link can open the file. Click 'More options' in that prompt to limit access to the message's recipients instead.
• In the Gmail app on a phone, tap 'Compose', then 'Attach', and choose 'Drive' from the menu.

Cause 2: Your Google storage is full

Personal accounts get up to 15 GB, shared among Drive, Gmail and Photos. Google says that if you reach your storage limit, you can't send or receive attachments, and its storage help adds that a full account can't upload files to Drive or send and receive email. That also closes off the Drive link route from Cause 1, so clear space first.

Items in Trash and Spam count against your limit until you permanently clear them. Google also says storage can take up to 48 to 72 hours to update after you delete multiple files, so the number may not drop straight away.

• Check your usage: in Drive on a computer, open 'Storage' from the left-hand menu.
• In the Gmail search box, type has:attachment larger:10M to find emails with attachments over 10 MB. Delete the ones you no longer need.
• Try older_than:2y has:attachment to find old attachments you have forgotten about.
• Empty Trash and Spam so the deleted items stop counting.

Cause 3: Your connection, proxy or network is blocking the upload

Reading email takes very little bandwidth, so Gmail can look perfectly healthy on a connection that can't finish a large upload. Google's Drive help calls a weak connection a common cause of many connection errors, and notes that customized firewall and proxy settings can sometimes block access to Drive, and that virus scanning software and ad blockers can interfere with Drive files.

• Turn your Wi-Fi or mobile data off, then back on, as Google suggests, and attach the file again.
• Try a different network, such as a phone hotspot. If the file uploads there, your original network is the cause.
• If you've set up a web browser proxy, try disabling it. Google lists this specifically for attachments that won't upload. Turn off any VPN as well for the test.
• Briefly pause an ad blocker or check your security software isn't blocking Google services, and turn it back on after the test.
• On a work or school network, ask the network administrator. If attachments show as unavailable, Google says your network administrator or internet provider may have blocked mail-attachment.googleusercontent.com, the domain it uses to host attachments.
• If Gmail itself is misbehaving, open the Google Workspace Status Dashboard to check for an outage. A 'Temporary Error (502)' message means Gmail is temporarily unavailable, and Google says it usually resolves itself quickly.

Cause 4: A browser extension, old cache or unsupported browser

If the same file uploads from your phone but not your computer, look at the browser. Google's upload checklist starts with using a supported browser and trying another one. Its 'Gmail won't load' help adds that extensions or add-ons may cause Gmail to not work, and suggests incognito mode and clearing cached data. Those steps aren't listed under upload failures specifically, but they are quick and worth trying.

Gmail works with browsers such as Chrome, Firefox, Safari and Microsoft Edge, and works best in the newest and last prior version of each. Cookies and JavaScript must be turned on. Clearing your data may sign you out of sites and make some load more slowly at first, so try it last.

• Open Gmail in an incognito or private window, as Google suggests, and attach the file. If it works there, an extension or stored browser data is the likely cause.
• In Chrome, click 'More' at the top right, then 'Extensions', then 'Manage extensions'. Switch extensions off one at a time, trying the upload after each.
• To clear data in Chrome, click 'More', choose 'Delete browsing data', pick a time range, tick 'Cookies and other site data' and the cached files option, then click 'Delete data'.
• Try the same file in a different browser. If it works there, you can send the email now and sort out the first browser later.

Cause 5: The Gmail app on your phone

To attach in the app, tap 'Compose', then 'Attach' at the top right, and pick the attachment type. If that stalls, Google's steps for the app are to make sure you have the most recent version of the Gmail app and to restart the device. On iPhone and iPad, it suggests testing your connection by opening a website in a browser such as Safari. It also says that if an Android device is low on storage space, the Gmail app doesn't sync, so free up space on the phone itself as well as in your Google account.

On Android, the last resort is Settings, then Apps, 'See All Apps', Gmail, 'Storage & cache', 'Clear storage'. Google warns to do this only if the other steps fail, because it can erase data held in the app, including drafts and your signature. Save anything important in your drafts somewhere else first.

Prevent it next time

A few habits stop most of these before they cost you a deadline.

• Treat 25 MB as a limit for the whole message, and send anything bigger as a Drive link from the start.
• Upload large files to Drive before you write the email, on a good connection, so the sending part takes seconds.
• Wait for the attachment to finish uploading before you press send, and don't start the same message on two devices.
• Run the has:attachment larger:10M search now and then, so a full account doesn't surprise you.
• Keep your browser updated, and if uploads start failing after you install an extension, turn that extension off first.

If you just need to hand over a large file

If the file is big and Google storage is the sticking point, OneSol Send takes files up to 5 GB by link, and the recipient doesn't need to sign in. Files are kept for 3 days and the sender needs a free OneSol account, so it suits a one-off handover rather than long-term storage.