Emails that get stuck in Outlook’s outbox usually happen because of a small problem, like a large attachment or a slow Internet connection.
However, if the emails keep getting stuck, then it’s likely caused by a mix of settings that Outlook doesn’t like or software that doesn’t work well with it.
The list below goes through most of these issues. Unfortunately, because this problem is so vague, you’ll have to go through them one by one to figure out which one is responsible.
Here are the most common fixes for Outlook emails that get stuck in the outbox:
- Poor Internet connection.
- The email attachment is too large.
- Send emails again from the Draft folder
- Recheck the email for malicious links or files
- Use the browser version
- Your Inbox folder is full
- Turn of ad blocker
- Turn off your VPN
- Flag Outlook as safe
- Check your antivirus
- Repair the Outlook desktop app
- Outlook app may not be updated
- Outlook might have an outage
Why Outlook emails get stuck in Outbox
1. Check your Internet connection
The simplest explanation should also be the first. If your Internet is sometimes wonky, it’s possible the connection isn’t stable enough for the email to be sent.
If you want to verify the stability of your connection (not its speed), check out this quick web page for a diagnostic: https://ping.canbeuseful.com/en#ping
2. Your attachment is too big
Outlook has a maximum attachment size of 20 MB. Normally, Outlook shouldn’t even allow you to attach files larger than this to an email since you will receive this warning pop-up:
If, however, you somehow managed to bypass this rule and attach a file even slightly larger than 20 MB, then it’s possible that Outlook’s servers act as a final failsafe and refuse to send the email and keep it in your Inbox.
To check if this is the case, either try sending the email again without an attachment or break up the attachment into multiple smaller files and send multiple emails.
If this works, you’ve found your culprit.
3. Try sending emails from Draft folder
It’s possible your emails aren’t sending because Outlook bugged out and isn’t telling you about it.
To fix this, try following the steps below. They should act as a sort of mini-reset and reestablish your connections to the Outlook servers:
In the Outlook app:
- Select the Send/Receive tab.
- Select Work Offline to stop Outlook from trying to send all emails.
- Select the Outbox.
- Move the email to the Drafts folder.
- Select the Send/Receive tab, and then select Work Offline to de-select it. This restarts your connection.
- Send the emails from the Draft folder.
4. Possible malicious links, files, or signatures
Big email providers such as Outlook or Gmail automatically scan every single attachment uploaded to their emails as a way to prevent users from sending viruses, malicious files, and even malicious links.
If your email contains links or files, it’s possible that Outlook scanned them and didn’t like them very much, so it prevents you from sending them by blocking them in the Outbox.
This can happen even if your files are completely legit and safe.
Here’s what Outlook has to say about this issue in their official documentation:
One of the most common ways of transmitting computer viruses is through file attachments. To help protect you and your recipients against computer viruses, Outlook blocks the sending and receiving of certain types of files (such as .exe and certain database files) as attachments.
5. Your Inbox folder is full
Outlook has a 50 GB limit on how many emails and files it can store.
According to Microsoft, if your inbox is full, you won’t be able to send or receive new messages.
A quick way to test this is to delete some unnecessary emails from your Junk or Drafts folders. After doing so, try sending an email once again.
If the email is successfully sent, then you’ve probably found the reason your emails were stuck in the Outbox.
You can also check the size of each individual folder in your Outlook account by right clicking on a folder -> Properties -> General Tab -> Folder Size.
Finally, if this was indeed the issue, then you can avoid deleting your files by increasing the 50 GB limit so you have more room to send emails.
To do this, follow this link.
6. Turn off your VPN
Another possibility is that your VPN interferes with Outlook, which causes issues when logging in or sending and receiving emails.
To troubleshoot this, try to turn off your VPN and see if your emails still get stuck in the Outbox.
If this was the problem but you really want to continue using both a VPN and Outlook at the same time, then try the fixes below and see if they remove any incompatibilities:
- Update and restart both Outlook and the VPN.
- Add an exception to the Windows Firewall for the VPN
- Disable the wireless network adapter (having a computer connected to both Wi-Fi and Ethernet can cause conflicts)
- Try changing your DNS settings.
- See if your internet router device allows for VPN traffic.
7. Disable Add-ins and run Outlook in safe mode
Some Outlook Add-ins, especially those not developed directly by Microsoft, might cause conflicts with the basic functionality of Outlook.
This is especially the case for Add-ins that have functionality to send or receive emails, since the Outbox and the Add-in share similar functionality.
To test this out, simply disable the Add-ins and restart Outlook and see if the problem persists.
You can view, enable, disable or remove by Add-ins through two methods:
- In Outlook app, go to Files -> Manage Add-ins.
- Also in Outlook app, go to Files -> Options -> Add-ins.
- On Outlook browser, go to any email -> Click the three “…” (next to the Reply, Reply All and Forward buttons) -> at the bottom, click the Add-ins button.
If the problem persists even after you’ve disabled all Add-ins, then try running your Outlook desktop app in safe mode by doing the following:
- Right-click the Start button, and click Run.
- Type Outlook.exe /safe, and click OK.
8. Check your antivirus
Antivirus programs are known to be very finicky and frequently consider legitimate software to be viruses or malicious software.
If you use antivirus software, then search for compatibility issues between your antivirus program and Outlook.
Every decent antivirus program should have a “whitelist” feature where you can prevent the antivirus from interfering with Outlook.
9. Repair the Outlook desktop app
All software can accumulate errors, and Outlook is no exception. The solution to this is to simply repair the Outlook installation.
To do this, go to Control Panel -> Programs -> Programs and Features. From there, select either Microsoft Outlook or the Microsoft software package that contains Outlook.
In my situation, Outlook is contained within Microsoft Office Professional Plus 2019.
Click “Change” and press Quick Repair. This will start the process of scanning and fixing each of Office programs, including Outlook.
10. Outlook might have an outage
Outlook is built and hosted on Microsoft’s Azure servers, so if Azure’s servers are having connectivity issues then Outlook will have connectivity issues too.
To see if Outlook has connectivity issues, you can either visit Outlook’s Twitter account at https://twitter.com/Outlook or go check on https://downdetector.com/status/outlook/ and see if other users are complaining about Outlook.
11. Outlook app may not be updated
Microsoft Office usually has automatic updates, but if you think your Outlook hasn’t updated automatically, you can update the app manually.
From within the Outlook app on desktop, go to File > Account (or Office Account if you opened Outlook). Under Product Information, choose Update Options > Update Now.
Note: You may need to click Enable Updates first if you don’t see the Update Now option right away. Close the “You’re up to date!”
12. Use the browser version instead of desktop app
If you still can’t find the issue that holds up your emails in the Outbox, try sending your emails from the browser version of Outlook at https://outlook.live.com/ .
Doing so should eliminate most of the technical issues that might exist on your device, since all of the work is done directly on Outlook’s servers instead.
13. Turn off your ad blocker
For Outlook users who use the app on Internet browsers, it’s possible that your ad blocker is causing conflicts with the Outlook website.
To fix this, try to whitelist https://outlook.live.com/ in your ad-blocker so it won’t conflict with the email service.