Outlook is not sending emails: quick troubleshooting guide

“Outlook not sending emails” is one of the most frequent problems in 2025, both in the desktop version (Outlook 2021/2019/Microsoft 365) and on the web (Outlook.com).

It often displays errors such as 0x8004010F, 0x800CCC0B, "Unable to connect to the server," or the message simply gets stuck in the Outbox. Check More Here: Windows update stuck at 0% – Solution

This step-by-step guide allows you to solve it in less than 10 minutes in 95% of cases, ordered from the simplest to the most technical.

Most common causes (2025)

Cause	Typical symptom	Frequency
Offline mode enabled	Airplane icon or “Working offline”	Very high
Password expired	Request credentials or error 0x8004010F	High
SMTP port blocked	Error 0x800CCC0E or “Timeout”	High
Corrupted data file	Message remains in Outbox	Media
Antivirus/firewall	Blocks port 587 or 465	Media
Attachment size	>20-25 MB (depends on the provider)	Low

Quick solutions (less than 5 minutes)

1. Check offline mode (the silliest and most common mistake)

• In Outlook desktop: tab Send/Receive → button Work offline (If it's highlighted in orange → deactivate it).
• In Outlook.com: bottom right → if it says “Offline” → click and activate connection.

2. Restart Outlook in safe mode

Close Outlook → Windows + R → writes:

outlook.exe /safe

If it sends now → the problem is an add-on. Go to File → Options → Plugins → COM → Manage → Disable all.

3. Empty the Output Tray

Sometimes a corrupted email or one with a very large attachment blocks everything.

1. Open the folder Outbox.
2. Select all messages (Ctrl + A).
3. Balance Delete or move them to Drafts.
4. Try sending a new, simple email.

4. Check the connection and the size of the attachment

• Try sending an email with no attachments and only text → if it works, the problem It's too large a file.
• Solution: Use OneDrive/WeTransfer or compress the file.

Intermediate solutions (5-10 minutes)

1. Repair the account (the solution that fixes 70% of cases)

1. File → Account Settings → Account Settings.
2. Select the problematic account → Repair.
3. Follow the wizard (Outlook automatically detects the servers in most cases: Gmail, Hotmail, Outlook.com, Office 365).

2. Change the SMTP port (works with almost all providers)

Many ISPs and public Wi-Fi networks block port 25.

1. File → Account settings → Manage profiles → Email accounts.
2. Select your account → Change → More settings → Advanced.
3. Change:
   • Outgoing server (SMTP) → 587
   • Encryption type → STARTTLS (or TLS)
   • Check “My outgoing server (SMTP) requires authentication” → “Use same settings as incoming server”.

Supplier	SMTP port	Encryption
gmail	587	STARTTLS
Outlook/Hotmail	587	STARTTLS
Office 365	587	STARTTLS
iCloud	587	STARTTLS
Local suppliers	465 or 587	SSL / TLS

3. Clear credential cache and log in again

1. Control Panel → User Accounts → Credential Manager.
2. Look for “Outlook”, “MicrosoftOffice16” or “mso” entries → Delete them.
3. Open Outlook → it will ask for your password again.

Advanced solutions (10-20 minutes)

1. Create a new Outlook profile

1. Control Panel → Mail (32-bit) → Show Profiles → Add.
2. Name it “NewProfile” → set up the account from scratch.
3. In “Always use this profile” → select the new one.

2. Repair the PST/OST file

1. Close Outlook.
2. Run: C:\Program Files (x86)\Microsoft Office\root\Office16\SCANPST.EXE
3. Select the .ost or .pst file from your account → Start repair.

3. Temporarily disable the antivirus/firewall

• Windows Defender → Virus & threat protection → Manage settings → Turn off real-time protection (5 minutes).
• Third-party antivirus (Avast, Kaspersky, Norton) → pause for 10 minutes and try again.

Quick table of errors and solutions (2025)

Error	Fastest solution
0x8004010F	Repair account or clear credential cache
0x800CCC0E / 0x800CCC0B	Change SMTP port to 587 + STARTTLS
Message stuck	Empty Output Tray or Safe Mode
Asks for password	Delete credentials or change password on the web
It doesn't send anything.	Check “Work offline”

Conclusion

In 95% of cases, Outlook Stop sending emails by:

1. Offline mode enabled
2. SMTP port blocked (change to 587 + STARTTLS)
3. Expired password or corrupted credential cache
4. Corrupted add-on or file

FAQS

1. Q: What is Outlook used for?
   A: It's an email client and personal information manager that handles email, calendar, contacts, tasks, and notes all in one application.
2. Q: How do I add a new email account to Outlook?
   A: Go to File > Add Account, enter your email and password, and follow the instructions to configure the server automatically or manually.
3. Q: How can I quickly search for emails?
   A: Use the search box at the top of Outlook. Refine your search using the tools (From, Subject, Contains attachments, Date) or use keywords and quotation marks for exact phrases.
4. Q: How do I organize email with rules?
   A: Home > Rules > Manage rules and alerts; then, create a rule (for example, move newsletters to a folder) and specify the conditions and actions.
5. Q: What are the best ways to manage my inbox overload?
6. A: Use the focused inbox (or sort by importance), set rules, archive old messages, unsubscribe from newsletters, and schedule a daily cleanup time.