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Email won't send? Fix mail stuck in the Outbox

Last reviewed: October 2026, against Google and Microsoft support pages · For Gmail, Outlook.com and the Outlook app on Windows.

You press Send, but the email sits in your Outbox, an error pops up, or it comes back with a “delivery failed” message. The usual causes are a lost connection, an attachment that's too big, a full mailbox, or a password that changed. These checks are free and none of them delete your mail.

Email coming in is the problem instead? See Email not arriving.

⚡ The short version

  1. Check you're online: open a website in your browser.
  2. Look for a big attachment. Open the oldest stuck email in the Outbox first and remove or shrink the attachment.
  3. Check your storage. A full account may not be able to send.
  4. Changed your password lately? Update it in your email app too.
  5. Got a “delivery failed” email? Read it. It says what went wrong.

Step by step

  1. Check your internet connection

    Open a web browser and go to any well-known website. If it won't load, the problem is your connection, not your email. See Internet not working?

    Classic Outlook on Windows: look at the bottom of the window. If it says Disconnected, Working Offline or Trying to connect…, select the Send / Receive tab and select Work Offline to go back online. You may need to open the stuck email and send it again.

    New Outlook for Windows: select Sync on the View tab.

  2. Look for a large attachment

    One big attachment can block that email and every email sent after it. Open your Outbox and open the oldest stuck email first. Microsoft says if its attachment is larger than 20 MB, remove it and attach a smaller file or a link instead.

    • Gmail: personal accounts can attach up to 25 MB. Bigger files are turned into a Google Drive link automatically.
    • Outlook.com: Microsoft says it can't send a message with an attachment larger than 25 MB.

  3. Check your storage

    • Gmail: your space is shared with Google Drive and Google Photos. Google says going over your storage can affect sending and receiving email, and you can't send or receive attachments. Check your space in the Google One storage manager (one.google.com/storage, or Manage storage in the Gmail app), then delete emails with big attachments you don't need and empty Trash and Spam.
    • Outlook.com: if your Microsoft storage is full, you can't send or receive email. Check it at Settings (gear) → Account → Storage.

  4. Changed your password? Update it in the app

    If you changed your password on the website, your email app on your computer or phone still has the old one. Microsoft says to update it in Outlook too. If Outlook keeps asking for it, or says to create an “app password,” see Outlook keeps asking for a password.

  5. Read the “delivery failed” email

    If the email left your Outbox but came back, you'll get an automatic reply that explains why. In Gmail it comes from Mail Delivery Subsystem, often with the subject Delivery Status Notification (Failure). Check your Spam folder for it too. Common reasons:

    • The address is wrong or doesn't exist. Look for typos, spaces or extra dots (for example gmal.con instead of gmail.com), and check you have the person's current address.
    • Their mailbox is full. They have to clear space before they can get new mail. Try again later or reach them another way.
    • Their server is busy or down. Send it again later.
    • It looked like spam to them. Remove links or text that ask for personal information. For a big group, Google suggests a Google Group instead of hundreds of addresses.

  6. Sent a lot of email today?

    • Gmail: personal accounts can't send more than 500 emails in a day, or one email to more than 500 people. Google says the block is temporary and lifts within 24 hours.
    • Outlook.com: Microsoft says brand-new accounts start with a low sending limit that goes up over time. Microsoft can also block an account for a while after unusual sign-in activity. If you can't sign in, see Can't sign in to your email.

Still stuck in classic Outlook on Windows?

Microsoft suggests these, from quickest to most involved:

  • Antivirus: some antivirus programs scan email and can block sending. Check with your antivirus maker.
  • Safe mode: an add-in can stop mail from sending. Press Windows + R, type outlook.exe /safe and select OK. If email sends in safe mode, see how to turn off add-ins.
  • Repair: repair Office, repair your Outlook profile, or run the Inbox Repair Tool. Microsoft's page in Sources has the steps.

On Outlook.com, Microsoft also suggests removing your email signature and trying again if you get an error.

Watch out: scammers send fake “your message couldn't be delivered” or “mailbox full” emails with a link to “fix” it. Don't click it. Check your Outbox and storage by going to Gmail or Outlook.com yourself. See Is this text, email or link a scam?

Sources

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