Outlook Not Sending Emails

Editorial Team·29 days ago

019513 minutes read

Quick answer: Outlook not sending emails is most often caused by a message stuck in the Outbox (large attachment or open compose window), Outlook running in offline mode, an SMTP connection failure, or an outdated account password. Checking the Outbox, toggling offline mode off (Send/Receive tab > Work Offline), and verifying SMTP settings resolves the majority of Outlook send failures.

"My Emails Are Sitting in the Outbox" — Why Outlook Stops Sending and How to Fix It

A situation that comes up regularly for Outlook users: a message is composed and sent, but it never arrives at the recipient. Checking the Sent Items folder shows the message is not there — it is sitting in the Outbox, with a status of "Sending" or no status at all. Or Outlook displays an error when the Send button is clicked, with a message about being unable to connect to the server. The problem is particularly frustrating when it is not immediately clear whether the message was sent or not — and whether the recipient is waiting for something that has not arrived. This guide covers the most common causes of Outlook not sending emails — on Windows, Mac, and Outlook on the web — and the steps to fix each one. The specific steps vary by Outlook version and account type (Microsoft 365, Exchange, Outlook.com, or a third-party IMAP/SMTP account); the troubleshooting logic applies broadly, and the exact menu paths may differ depending on the Outlook version in use.

Why Outlook Stops Sending — The Most Common Scenarios

Outlook's send process involves several steps: the message is placed in the Outbox, Outlook connects to the outgoing mail server (SMTP), authenticates, and transfers the message. If any step in this process fails, the message remains in the Outbox and is not delivered. The failure can occur at the connection stage (Outlook cannot reach the SMTP server), the authentication stage (the server rejects the credentials), or the transfer stage (the message is too large, or the server rejects it for another reason). Offline mode is a common and easily overlooked cause. Outlook has a "Work Offline" mode that disconnects it from the mail server — useful when working without an internet connection, but easy to activate accidentally. When offline mode is active, messages are queued in the Outbox but not sent, and Outlook does not display a prominent warning that it is offline. The status bar at the bottom of the Outlook window shows "Working Offline" when this mode is active, but this indicator is easy to miss. A stuck message in the Outbox can also block subsequent messages from being sent. Outlook processes the Outbox sequentially — if the first message in the Outbox is stuck (due to a large attachment, an open compose window, or a connection failure), subsequent messages queue behind it and are not sent until the stuck message is resolved. This means that a single problematic message can prevent all outgoing email from being delivered.

Outlook Not Sending Emails — 5 Common Causes and Fixes

SymptomLikely CauseFixMessage stuck in OutboxLarge attachment / open compose windowGo offline; delete stuck message; resendOutlook shows "Working Offline"Offline mode enabledSend/Receive tab > Work Offline (toggle off)Cannot connect to serverWrong SMTP settings or firewallVerify SMTP settings; check firewallAuthentication error on sendPassword changed or app password neededUpdate password in account settingsSend works in web but not desktopOutlook add-in or profile corruptionDisable add-ins; create new profile

1. Message Stuck in the Outbox

A message stuck in the Outbox is the most common cause of Outlook appearing not to send. Messages get stuck for several reasons: the message has a very large attachment that is taking too long to upload and the connection timed out; the message is currently open in a compose window (Outlook cannot send a message that is open for editing); Outlook lost its connection to the SMTP server partway through the send process; or the message was flagged by the server for a policy violation (such as exceeding the server's message size limit). To resolve a stuck Outbox message: first, switch Outlook to offline mode (Send/Receive tab > Work Offline) to prevent Outlook from repeatedly attempting to send the stuck message. Close any open compose windows. Open the Outbox folder and check whether the stuck message is open — if it is, close it. Then right-click the stuck message and select Delete, or open it and reduce the attachment size before resending. After resolving the stuck message, switch back to online mode and allow Outlook to process the Outbox. If the message cannot be deleted while Outlook is running, closing and reopening Outlook sometimes releases the lock.

2. Outlook Is in Offline Mode

Outlook's offline mode is activated by clicking "Work Offline" in the Send/Receive tab, or automatically when Outlook detects that the internet connection is unavailable. When offline mode is active, Outlook queues outgoing messages in the Outbox but does not attempt to send them. The status bar at the bottom of the Outlook window displays "Working Offline" — but this indicator is small and easy to miss, particularly on large monitors. To disable offline mode, go to the Send/Receive tab in the Outlook ribbon and click "Work Offline." If the button appears highlighted or pressed (indicating offline mode is active), clicking it toggles back to online mode. After switching to online mode, Outlook should automatically attempt to send any messages in the Outbox. If Outlook immediately switches back to offline mode, the internet connection may be unavailable — check the connection and try again. On Mac, the equivalent setting is in the Outlook menu > Work Offline.

3. SMTP Server Connection Failure

If Outlook displays a "Cannot connect to server" or "The operation timed out waiting for a response from the sending (SMTP) server" error, the problem is with the connection to the outgoing mail server. Common causes are incorrect SMTP settings (wrong hostname, port, or encryption), a firewall or antivirus blocking the SMTP port, or the mail server being temporarily unavailable. Verifying the SMTP settings against the provider's current documentation is the first step — for Microsoft 365 and Exchange accounts, the SMTP settings are typically configured automatically, but for IMAP/SMTP accounts (Gmail, Yahoo, etc. configured in Outlook), the settings may need to be verified manually. For Gmail configured in Outlook as an IMAP/SMTP account: SMTP server smtp.gmail.com, port 587 (STARTTLS) or 465 (SSL), authentication required, username is the full Gmail address, password is an app password if 2FA is enabled. For Outlook.com accounts: SMTP server smtp.office365.com, port 587, STARTTLS, authentication required. After verifying settings, test the connection using the "Test Account Settings" button in Outlook's account settings dialog (File > Account Settings > Account Settings > [Account] > Change > Test Account Settings).

4. Account Password Changed or Authentication Error

If the email account password was recently changed — through the provider's web interface, by an IT administrator, or through an organization's password policy — Outlook continues to use the old stored password for SMTP authentication. The result is an authentication error when Outlook attempts to send, which may appear as a password prompt or as a send failure without a visible prompt. Updating the password in Outlook's account settings resolves this: go to File > Account Settings > Account Settings, select the affected account, click Change, and update the password field. For Microsoft 365 accounts, the password update may need to be done through the Microsoft account sign-in flow rather than a simple password field — the Change button may open a browser-based authentication window. For Gmail accounts with 2FA enabled, the SMTP password in Outlook should be an app password (generated at myaccount.google.com/apppasswords), not the regular account password. If the regular account password was recently changed, the app password remains valid — app passwords are independent of the account password and do not need to be regenerated when the account password changes.

5. Outlook Add-In Conflict or Corrupted Profile

⚠️ Worth checking if other fixes have not worked: Outlook add-ins — third-party extensions that add functionality to Outlook — can occasionally interfere with the send process. If Outlook sends successfully in Outlook on the web (outlook.office.com or outlook.live.com) but not in the desktop application, an add-in conflict or a corrupted Outlook profile is a likely cause. To test for add-in conflicts, start Outlook in safe mode by holding the Ctrl key while clicking the Outlook icon, or by running `outlook.exe /safe` from the Run dialog. If Outlook sends successfully in safe mode, an add-in is the cause — disable add-ins one at a time (File > Options > Add-ins > Manage: COM Add-ins > Go) to identify the conflicting one. If safe mode does not resolve the issue, creating a new Outlook profile (Control Panel > Mail > Show Profiles > Add) and re-adding the account may resolve a corrupted profile.

Step-by-Step: How to Fix Outlook Not Sending Emails

Step 1: Check the Outbox and Offline Mode Status

Open Outlook and check the Outbox folder — if messages are present, they have not been sent. Check the status bar at the bottom of the Outlook window for "Working Offline." If offline mode is active, go to the Send/Receive tab and click "Work Offline" to toggle it off. After switching to online mode, wait 30 seconds and check whether the Outbox clears. If messages remain in the Outbox after switching to online mode, proceed to the next step.

Step 2: Resolve Stuck Outbox Messages

Switch Outlook to offline mode (Send/Receive tab > Work Offline). Close any open compose windows. Open the Outbox folder and check whether any messages are open — close them if so. Right-click the stuck message and select Delete, or open it to reduce the attachment size. If the message cannot be deleted, close Outlook completely, wait 30 seconds, and reopen it — then attempt to delete the stuck message again. After clearing the Outbox, switch back to online mode and compose a short test message to confirm sending is working.

Step 3: Verify SMTP Settings and Test the Connection

Go to File > Account Settings > Account Settings, select the affected account, and click Change. Verify the outgoing mail server settings against the provider's current documentation. Click "Test Account Settings" to test the connection — Outlook will attempt to connect to both the incoming and outgoing servers and report any errors. If the outgoing server test fails, note the error message and compare the SMTP settings to the provider's documentation. Correct any discrepancies and test again.

Step 4: Update the Account Password

If the account password was recently changed, update it in Outlook's account settings. Go to File > Account Settings > Account Settings, select the affected account, click Change, and update the password field with the current password. For Microsoft 365 accounts, the Change button may open a browser-based authentication window — complete the sign-in process in the browser. For Gmail accounts with 2FA, confirm that the SMTP password is an app password (not the regular account password) and that the app password is still valid. After updating the password, test sending a message.

Step 5: Test in Safe Mode and Check Add-Ins

If the previous steps have not resolved the issue, test whether Outlook sends successfully in safe mode. Hold the Ctrl key and click the Outlook icon to start in safe mode (or run `outlook.exe /safe` from the Run dialog). Compose and send a test message in safe mode. If sending works in safe mode, an add-in is the cause — go to File > Options > Add-ins > Manage: COM Add-ins > Go and disable all add-ins, then re-enable them one at a time to identify the conflicting one. If sending does not work in safe mode, create a new Outlook profile (Control Panel > Mail > Show Profiles > Add) and re-add the account.

Frequently Asked Questions — Outlook Not Sending Emails

Why is Outlook not sending emails?

The most common causes are a message stuck in the Outbox, Outlook running in offline mode, an SMTP connection failure, an outdated account password, or an add-in conflict. Checking the Outbox and toggling offline mode off (Send/Receive tab > Work Offline) are the fastest first steps.

Why is my email stuck in the Outlook Outbox?

Messages get stuck in the Outbox because of a large attachment, an open compose window, a lost connection during sending, or offline mode being active. Switch to offline mode, close any open compose windows, delete the stuck message, and switch back to online mode to resolve it.

How do I fix Outlook working offline?

Go to the Send/Receive tab in the Outlook ribbon and click "Work Offline" to toggle offline mode off. The status bar at the bottom of the Outlook window shows "Working Offline" when offline mode is active. After switching to online mode, Outlook should automatically attempt to send any messages in the Outbox.

Why does Outlook say "Cannot connect to server" when sending?

This error indicates Outlook cannot reach the SMTP server. Common causes are incorrect SMTP settings, a firewall blocking the SMTP port, or an unstable internet connection. Verifying SMTP settings against the provider's documentation and using the "Test Account Settings" button in account settings identifies the specific issue.

How do I delete a stuck message from the Outlook Outbox?

Switch Outlook to offline mode (Send/Receive tab > Work Offline), close any open compose windows, open the Outbox folder, right-click the stuck message, and select Delete. After deleting, switch back to online mode. If the message cannot be deleted while Outlook is running, close and reopen Outlook and try again.

Conclusion & My Take

Outlook not sending emails is almost always caused by one of a small number of issues — a stuck Outbox message, offline mode, an SMTP connection failure, or a password problem — and each has a straightforward fix. The most important diagnostic step is checking the Outbox and the offline mode status first, because these two causes account for the majority of Outlook send failures and are resolved in under a minute when identified. The add-in conflict scenario is worth knowing about because it produces a symptom — Outlook sends in the web interface but not the desktop app — that can be confusing without knowing to look for it. Starting Outlook in safe mode is the fastest way to confirm or rule out an add-in as the cause, and it requires no permanent changes to the Outlook configuration. If safe mode resolves the issue, disabling add-ins one at a time identifies the specific one causing the conflict without requiring a full Outlook reinstallation. Have you encountered an Outlook send failure that was caused by something not covered here, or found a fix that worked for a specific Outlook version or account type? Outlook's behavior varies between versions and account types — feel free to share your experience in the comments below.