Fixing Outlook Problems: Common Errors
Struggling with fixing Outlook problems that just won't go away? From synchronization issues to error messages, Outlook can sometimes be pretty frustrating. In this article we help you with fixing Outlook problems by discussing the most common issues and their solutions.
Is Outlook not working the way it should? Error messages when sending, problems receiving mail, or strange certificate warnings? In this article we cover the 10 most common Outlook problems and show you how to solve them. Whether you use Outlook 365, Outlook 2021 or an older version, these solutions work for all versions.
Theory7 Server Settings
Before we cover the problems, first the correct server settings for Theory7 hosting. Many problems arise from incorrect settings, so check these first.
| Setting | IMAP (Recommended) | POP3 (Alternative) |
|---|---|---|
| Incoming server | mail.theory7.net | mail.theory7.net |
| Incoming port | 993 (SSL/TLS) | 995 (SSL/TLS) |
| Outgoing server (SMTP) | mail.theory7.net | mail.theory7.net |
| Outgoing port | 465 (SSL/TLS) or 587 (STARTTLS) | 465 (SSL/TLS) or 587 (STARTTLS) |
| Username | Your full email address | Your full email address |
| Authentication | Password (normal authentication) | Password (normal authentication) |
Important: Always use your full email address as the username, so for example info@yourdomain.com, not just info.
1. Connection error: cannot connect to server
This is the most common error message in Outlook. The message "A connection to the server could not be established" can have several causes.
Possible causes and solutions
- Internet connection: Check whether you're connected to the internet. Open a website in your browser to test this.
- Firewall or antivirus: Some security software blocks Outlook. Add Outlook to your firewall's exceptions or temporarily disable your antivirus to test.
- Wrong server name: Check that you have entered exactly
mail.theory7.net, without typos or extra spaces. - VPN active: A VPN can sometimes block mail connections. Temporarily disable your VPN to test.
How to check the server settings in Outlook
- Go to File > Account Settings > Account Settings
- Select your email account and click Change
- Click More Settings > the Advanced tab
- Check the server names and port numbers according to the table above
2. Outlook keeps asking for a password
Does Outlook keep asking for your password, even after you've entered it correctly? This frustrating problem often has a simple solution.
Solutions
- Save the password again: Remove the saved password and enter it again. Check "Remember password".
- Clear Windows Credential Manager:
- Open the Windows Control Panel
- Go to Credential Manager > Windows Credentials
- Look for any entries with Outlook or your mail server
- Remove these and enter your password again in Outlook
- Reset password: Log in to DirectAdmin and reset your email password. Use the new password in Outlook.
- Check authentication method: Make sure "Normal password authentication" is selected, not OAuth2 or other methods.
3. Sending email fails (SMTP error)
Can you receive email but not send it? Then something is probably wrong with your SMTP settings (outgoing mail).
Common error codes
- Error 550: Sender not authorized. Check whether SMTP authentication is enabled.
- Error 553: Email address not allowed. Check whether your sender address is correct.
- Error 421/451: Temporary server error. Try again later.
Enabling SMTP authentication
- Go to File > Account Settings > Account Settings
- Select your account and click Change
- Click More Settings
- Go to the Outgoing Server tab
- Check: My outgoing server (SMTP) requires authentication
- Select: Use same settings as my incoming mail server
- Click OK and Next to test
4. Certificate warning or security message
Do you get a warning that the security certificate doesn't match the server name? This is usually because you're not using the correct server name.
Why do you see this warning?
The SSL certificate is issued for mail.theory7.net. If you use a different server name (such as mail.yourdomain.com), the certificate doesn't match and Outlook shows a warning.
Solution
Change your server settings so you use mail.theory7.net everywhere:
- Go to File > Account Settings > Account Settings
- Select your account and click Change
- Change both the incoming and outgoing server to:
mail.theory7.net - Click More Settings > Advanced
- Check that the encryption type is set to SSL/TLS
After this change, the certificate warning should disappear.
5. Emails don't sync (IMAP problems)
Do you see different emails in Outlook than in webmail? Or are sent emails not being saved? These are synchronization problems that often occur with IMAP accounts.
Checking the folder structure
- Go to File > Account Settings > Account Settings
- Select your IMAP account and click Change
- Click More Settings > the Advanced tab
- Check the Root folder path. Leave this field empty or enter
INBOX - Set the correct folders for:
- Sent items: Sent (or INBOX.Sent)
- Trash: Trash (or INBOX.Trash)
- Drafts: Drafts (or INBOX.Drafts)
Manual synchronization
Right-click your Inbox and choose IMAP Folders > Subscribe. Select all the folders you want to see and click OK. Then press F9 or click Send/Receive to synchronize.
6. Outlook freezes or stops responding
Does Outlook freeze during startup or during use? This can be caused by a damaged profile, too much data, or conflicting add-ins.
Quick fixes
- Start Outlook in safe mode: Press Windows+R, type
outlook.exe /safeand press Enter. If Outlook now works, an add-in is the culprit. - Disable add-ins: Go to File > Options > Add-ins. Disable suspicious add-ins.
- Rebuild the OST file: Close Outlook. Rename the .ost file (look for
*.ostin your AppData folder). Restart Outlook, the file will be recreated automatically.
7. Attachments cannot be opened or sent
Attachment problems are annoying. Sometimes you can't open them, sometimes you can't send them.
Cannot open attachments
- Check whether you have the right program to open the file type
- Right-click the attachment and choose Save As. Then open the file from the saved location
- Check your antivirus - some block certain file types
Cannot send attachments
- File size: Theory7 allows attachments up to 35 MB per email. Larger files must be sent via another method
- Blocked file types: Outlook blocks certain file types by default (.exe, .bat). Pack these files into a ZIP file
8. Search in Outlook doesn't work
Can't find emails even though you're sure they exist? Outlook's search index may be corrupted or incomplete.
Rebuilding the search index
- Go to File > Options > Search
- Click Indexing Options
- Click Advanced
- Click Rebuild
- Wait for the process to finish (this can take several hours for large mailboxes)
9. Error code 0x800CCC... (various errors)
Outlook uses error codes that start with 0x800CCC. Here are the most common ones and their solution:
| Error code | Meaning | Solution |
|---|---|---|
| 0x800CCC0D | Server not found | Check server name (mail.theory7.net) |
| 0x800CCC0E | Connection to server failed | Check ports and SSL settings |
| 0x800CCC0F | Connection dropped by server | Increase timeout in advanced settings |
| 0x800CCC90 | POP3 authentication error | Check username and password |
| 0x800CCC92 | Wrong username/password | Reset password in DirectAdmin |
10. Last resort: create a new Outlook profile
If nothing else works, creating a new Outlook profile can be the solution. This fixes problems caused by a damaged profile.
Creating a new profile
- Close Outlook completely
- Open the Control Panel
- Search for Mail and open it
- Click Show Profiles
- Click Add and give the profile a name
- Follow the wizard to add your email account again
- Select the new profile as default
- Start Outlook
Note: With IMAP, all your emails remain preserved on the server. With POP3, emails can be lost if they were only stored locally.
Bonus: tips to prevent problems
Prevention is better than cure. Here are some tips to keep Outlook running smoothly:
- Keep Outlook up to date: Install updates regularly via Windows Update or the Microsoft 365 app
- Archive old emails: A full mailbox slows Outlook down. Archive emails older than a year
- Limit the number of add-ins: Every add-in slows Outlook down. Remove what you don't use
- Use IMAP: IMAP synchronizes with the server, keeping your emails always safe
- Back up regularly: Periodically export your Outlook data to a PST file
More about email
Outlook problems are often related to email settings. Also check out:
- Business email hosting at Theory7
- Setting up SPF, DKIM and DMARC - prevent spam problems
- Setting up email forwarding
- Setting up email on iPhone
Need help?
Still running into problems after trying these solutions? Our support team is ready to help. Get in touch through the customer portal or send an email. Mention in your message which error you see and which steps you've already tried. This helps us help you faster.
Fixing Outlook problems: overview of errors
When fixing Outlook problems, it's important to recognize the right error code. Below you'll find the most common errors and how to resolve them.
| Error code | Cause | Solution |
|---|---|---|
| 0x800CCC0E | Server connection error | Check SMTP settings |
| 0x800CCC0F | Server timeout | Increase timeout value |
| 0x800CCC90 | Authentication error | Re-enter password |
| 0x80040154 | Damaged profile | Create a new Outlook profile |
| 0x8004010F | Corrupt PST file | Repair PST with ScanPST |
Steps for effectively fixing Outlook problems
- First check your internet connection when fixing Outlook problems
- Verify that your email address and password are entered correctly
- Check the server settings at your web hosting provider
- Use Microsoft's built-in repair tool for fixing Outlook problems
- Create a new Outlook profile if the existing profile is damaged
- Consider a professional email address setup for better compatibility
- Check your domain name DNS records for persistent sending problems
You can fix most Outlook problems yourself with the right knowledge. Contact your hosting provider if you still experience problems after following these steps.
Fixing Outlook Problems: Synchronization Errors
Synchronization errors are among the most frustrating issues when using Outlook. Below we discuss the causes and solutions for the most common synchronization problems when fixing Outlook problems.
IMAP synchronization problems
If Outlook isn't syncing with your IMAP server, first check whether you have an active internet connection. Then open Outlook in safe mode by starting it with the /safe parameter. If the problem disappears in safe mode, it's caused by an add-in. Disable add-ins one by one to identify the culprit. Also check your folder subscription: in Outlook you can subscribe to specific IMAP folders. If a folder doesn't appear, you may not be subscribed to it.
Offline address book errors
With Exchange accounts, the offline address book can cause synchronization errors. You resolve the error about synchronizing the offline address book by deleting the OAB file and downloading it again. Navigate to the Offline Address Books folder in your Outlook profile folder and delete the contents. Restart Outlook and the address book will automatically download again from the Exchange server.
Common error codes and solutions
| Error code | Meaning | Solution |
|---|---|---|
| 0x800CCC0E | Cannot connect | Check server settings and ports |
| 0x800CCC0F | Connection dropped by server | Increase timeout settings |
| 0x8004010F | Outlook data file not accessible | Repair or create a new profile |
| 0x80042108 | Cannot connect to incoming mail server | Check IMAP or POP3 settings |
| 0x800CCC1A | Security handshake failed | Update SSL/TLS settings |
Fixing Outlook Problems: Performance Improvement
A slow-running Outlook can seriously affect your productivity. With the following optimizations you'll resolve the most common performance problems when fixing Outlook problems.
Optimizing the PST/OST file
The Outlook data file can become large and fragmented over time, leading to slower performance. Compact the file via File, Account Settings, Data Files and then Settings to compress it. Keep the file smaller than 10 GB for optimal performance. Archive old emails regularly to a separate PST file via the AutoArchive feature. Keep only recent email in your primary mailbox for the best performance.
Managing add-ins for better speed
Add-ins can significantly slow down Outlook during startup and daily use. Go to File, Options and Add-ins to see which add-ins are active. Disable all non-essential add-ins and test whether performance improves. Then add add-ins back one at a time to identify which has the most impact on speed. Common culprits are outdated antivirus integrations, social media plugins and unused business software connectors.
Also having problems with your webmail? Check out our article on setting up webmail with Outlook for configuration tips.
Fixing Outlook Problems: Preventive Maintenance
Many Outlook problems can be prevented with regular preventive maintenance. By proactively maintaining your Outlook installation, you minimize the chance of unexpected problems.
Monthly maintenance schedule
- Week 1: Remove old and unnecessarily kept emails and fully empty the Deleted Items folder
- Week 2: Compact your PST/OST file to reduce fragmentation and free up storage space
- Week 3: Check and update all installed add-ins to the latest versions
- Week 4: Back up your Outlook data file and store it in an external location
Keeping Outlook up to date
Microsoft regularly releases updates for Outlook that close security holes and fix bugs. Make sure automatic updates are enabled via File, Office Account and Update Options. Check monthly that all updates are installed. Outdated versions of Outlook may be incompatible with modern mail servers that require TLS 1.2 or higher, leading to connection problems.
When a new profile is the best solution
If you regularly experience recurring problems that keep coming back after a temporary fix, creating a new Outlook profile is often the definitive solution. A new profile replaces all configuration files with fresh versions. First export your contacts and calendar items, then create a new profile via Control Panel, Mail and Show Profiles. Reconfigure your email accounts and import your previously exported data.
Fixing Outlook Problems: Summary and Resources
To efficiently resolve your Outlook problems, it helps to follow a structured approach and know where to turn for help.
Step-by-step troubleshooting
Follow a systematic approach for every Outlook problem for the fastest solution. Start with the simplest solutions: restart Outlook, check your internet connection and verify your account settings. Then try starting Outlook in safe mode to check whether add-ins are causing the problem. If the problem persists, repair your Outlook profile via the Control Panel. For damaged data files, use the Inbox Repair Tool. If none of these steps work, create a completely new Outlook profile.
Where to seek help for persistent problems
If you can't solve the problem yourself, there are several resources available. The Microsoft Support Community offers an active forum where users and Microsoft staff help with Outlook problems. Your hosting provider can help with server-related issues such as IMAP configuration and SSL settings. For business environments with Exchange Server, your IT department is the first point of contact. Also consider hiring an IT specialist if you regularly run into complex problems that affect your productivity.
Fixing Outlook Problems: Advanced Diagnostics
When standard solutions don't work, advanced diagnostic methods help with fixing Outlook problems. Microsoft's built-in diagnostic tools provide detailed information about connection status and error codes. Open the Connection Status window via Ctrl+click on the Outlook icon in the system tray to view real-time connection data. The Microsoft Support and Recovery Assistant is a free tool that automatically detects and fixes common Outlook problems. Also use the Windows Event Viewer to identify Outlook-related errors and warnings that point toward the right solution.
When to bring in professional help
Not all Outlook problems can be solved yourself. Bring in professional help when you repeatedly get the same error message despite following all standard solutions. A specialist is also advisable in case of data loss or corrupt PST files, as they can deploy specialized recovery tools. Your IT department or hosting provider can diagnose server-side configuration problems that aren't visible from the client. Invest in professional support when your team's productivity is being affected by persistent email problems.
In summary, successfully fixing Outlook problems requires a systematic approach: start with the simplest solutions and work step by step toward more complex diagnostics. Document which steps you've taken and what the result was, so you can reach a solution faster for recurring problems.
