CyberPanel Hosting

• In the address bar, type: https://:8090
• Replace with your actual server IP address.
• If you encounter an SSL warning (common for self-signed certs on first login), proceed by accepting the risk (e.g., "Advanced" -> "Proceed to...").

• On the CyberPanel login page, enter your Username (e.g., admin).
• Enter your Password.
• Click "Sign In":
• You're In! You should now see the CyberPanel dashboard.

• LiteSpeed Web Server Management (Server Status)
• WordPress Staging/Cloning (under Websites → Manage)
• File Manager (under Websites → Manage)
• Git Manager (under Websites → Manage)

• For the root domain (e.g., yourdomain.com):
  • Click "+ Add record"
  • Type: A
  • IPv4 address: Enter your CyberPanel server's IP address
  • Proxy status: Start with "DNS only" (grey cloud) for testing
  • Click "Save"
• For www subdomain (e.g., www.yourdomain.com):
  • Click "+ Add record"
  • Type: A (or CNAME if you prefer)
  • Name: www
  • IPv4 address (if A record): Enter your CyberPanel server's IP address
  • Target (if CNAME record): Enter @ or yourdomain.com
  • Proxy status: "DNS only" for now
  • Click "Save"

• yourdomain.com A 192.0.2.1 (Points your main website to the server)
• blog.yourdomain.com A 192.0.2.2 (Points a subdomain to a server)

• Priority: A lower number means higher priority. Mail is tried at the lowest priority server first.
• Value/Target: The hostname of the mail server (e.g., mail.yourdomain.com or aspmx.l.google.com).

• yourdomain.com MX 10 mail.yourdomain.com
• yourdomain.com MX 20 backupmail.yourdomain.com

• www.yourdomain.com CNAME yourdomain.com
• shop.yourdomain.com CNAME myshopifyprovider.com

• SPF (Sender Policy Framework): Helps prevent email spoofing. v=spf1 mx a -all
• DKIM (DomainKeys Identified Mail): Cryptographically signs emails. Contains a public key.
• DMARC (Domain-based Message Authentication, Reporting & Conformance): Email authentication policy.
• Domain Ownership Verification: For services like Google Search Console, Microsoft 365.

• yourdomain.com TXT "v=spf1 mx -all"
• _dmarc.yourdomain.com TXT "v=DMARC1; p=reject; rua=mailto:dmarc@yourdomain.com"

• Find the DNSSEC section and click "Enable DNSSEC" or a similar button
• Cloudflare will generate the necessary DS (Delegation Signer) records

• Cloudflare will display the DS record information (Key Tag, Algorithm, Digest Type, Digest)
• You'll need these for your registrar

• This varies greatly by registrar
• Look for "DNSSEC," "DS Records," or similar in your domain management area
• Namecheap: Domain List -> Manage -> Advanced DNS -> DNSSEC section
• GoDaddy: My Products -> Domain -> Manage DNS -> Advanced Settings (bottom of page) -> DNSSEC

• Carefully enter the Key Tag, Algorithm, Digest Type, and Digest provided by Cloudflare into your registrar's interface
• Save the changes

• Back in Cloudflare, it might take some time for the status to update to "Active" or "Success"
• You can also use an online DNSSEC checker tool (like DNSViz or Verisign DNSSEC Debugger) to test your domain after a few hours

• Username: Enter the desired part before the @ (e.g., info, support, john.doe)
• Password: Create a strong password or use the "Generate" button
• Disk Quota (Optional): Set a limit for mailbox size (in MB). 0 for unlimited

• Open your web browser and go to: https:///rainloop/ (or /snappymail/ if that's the installed webmail client)
• It's better to use https://yourdomain.com/rainloop/ once SSL is set up for your domain

• Log in to CyberPanel
• Navigate to "Email" -> "Access Webmail"
• This will redirect you to the webmail login page

• Email: Enter your full email address (e.g., info@yourdomain.com)
• Password: Enter the password for that email account
• Click "Login" or the arrow button

• Go to your DNS provider (Cloudflare, Namecheap, GoDaddy, or CyberPanel -> DNS -> Add/Edit Records if CyberPanel is authoritative)
• Look for a TXT record for your root domain (@ or yourdomain.com)
• A common SPF record for CyberPanel: v=spf1 a mx ip4: ~all (or -all for stricter policy)
  • a: Allows the server IP defined in your domain's A record
  • mx: Allows servers listed in your MX records
  • ip4:: Explicitly allows your server's IP
  • ~all (SoftFail): Emails from other sources might be marked suspicious
  • -all (HardFail): Emails from other sources should be rejected
• Add or modify the TXT record

• In CyberPanel, go to "Email" -> "DKIM Manager"
• Select your domain. It should show DKIM keys are active/generated
• For External DNS (e.g., Cloudflare):
  • 1. In DKIM Manager, CyberPanel will display the TXT record name (e.g., default._domainkey.yourdomain.com) and the value (the public key)
  • 2. Copy this name and value
  • 3. Go to your DNS provider and create a new TXT record with this name and value
  • 4.
  • 5.

• Go to your DNS provider
• Create a TXT record with the name _dmarc.yourdomain.com (or just _dmarc if your provider auto-appends the domain)
• Value (start simple): v=DMARC1; p=none; rua=mailto:your-email@yourdomain.com
  • p=none: Monitor mode. No action taken on failing emails. Good for starting
  • rua=mailto:your-email@yourdomain.com: Aggregate reports will be sent to this address
• Later, you can change p=none to p=quarantine or p=reject

• Server: mail.yourdomain.com (or your server hostname/IP)
• Port: 993 (SSL/TLS) or 143 (STARTTLS/None)
• Encryption: SSL/TLS or STARTTLS

• Server: mail.yourdomain.com (or your server hostname/IP)
• Port: 465 (SSL/TLS) or 587 (STARTTLS/None)
• Encryption: SSL/TLS or STARTTLS
• Requires authentication (use same username/password as incoming)

• Under "Send mail as," click "Add another email address"
• Enter your Name and Email Address. Keep "Treat as an alias" checked. Click "Next Step"
• Enter SMTP Server (e.g., mail.yourdomain.com), Port (587 or 465), Username (full email), Password. Select SSL or TLS. Click "Add Account"
• Gmail will send a verification email. Check your CyberPanel webmail, get the code, and enter it

• Incoming mail (IMAP): Server, Port 993, Encryption: SSL/TLS
• Outgoing mail (SMTP): Server, Port 465 (or 587), Encryption: SSL/TLS (or STARTTLS)
• Ensure "Outgoing server requires authentication" is checked and uses same settings as incoming

• You might see options for "Hostname SSL" (for the server hostname itself) and "Mail Server SSL" on a different page (SSL -> MailServer SSL). For a website, you're typically on the website's manage page
• Select the domain(s) you want to include (usually yourdomain.com and www.yourdomain.com)
• Click the "Issue SSL" button

• Cause A: DNS Not Propagated: Let's Encrypt cannot verify domain ownership if DNS A records aren't pointing correctly to your server or haven't propagated globally.
  • Solution: Use a DNS checker tool (like dnschecker.org) to confirm your domain and www subdomain point to the correct server IP from multiple locations. Wait longer for propagation if needed.
• Cause B: Incorrect Web Server Configuration / .htaccess block: Sometimes existing .htaccess rules or web server configs can interfere with Let's Encrypt's .well-known/acme-challenge validation path.
  • Solution: Temporarily rename or disable .htaccess files in your website's public_html directory and try issuing SSL again. Check OpenLiteSpeed vHost config for any conflicting rules.
• Cause C: Rate Limits: Let's Encrypt has rate limits (e.g., 50 certs per registered domain per week).
  • Solution: Wait for the rate limit to reset. Use the staging environment for testing if you're issuing many certs.
• Cause D: Firewall Blocking: Server or Cloudflare firewall might block Let's Encrypt validation servers.
  • Solution: Temporarily disable CSF or ModSecurity, or whitelist Let's Encrypt IPs if known. Ensure port 80 is open, as HTTP-01 challenge uses it.

• Cause: The page is loaded via HTTPS, but some resources (images, scripts, CSS) are still loaded via HTTP.
• Solution:
  • Update all internal links/resource URLs in your website code/CMS to use https:// or relative paths (/images/pic.jpg).
  • Use a plugin (e.g., Really Simple SSL for WordPress) to help fix mixed content.
  • Check browser developer console (F12) "Console" tab for specific mixed content errors.

• Cause A: Cron Job Issues: The CyberPanel cron job for renewal might not be running.
  • Solution: Check cron logs. Ensure cron daemon is active. Manually try to renew SSL for a domain via CyberPanel to see if it works.
• Cause B: DNS Changed: If DNS records were changed after initial issuance, renewal might fail.
  • Solution: Ensure DNS is still pointing correctly.
• Cause C: Old CyberPanel Version: Older versions might have bugs.
  • Solution: Update CyberPanel to the latest version.

• Cause: Mismatch in supported SSL/TLS protocols or cipher suites between browser and server.
• Solution:
  • Ensure OpenLiteSpeed is updated.
  • Check OpenLiteSpeed SSL configuration (usually defaults are fine). This is more advanced.
  • Try a different browser or clear browser cache/SSL state.

• Issue: Email clients show certificate warnings.
• Solution:
  • Ensure mail.yourdomain.com has an A record pointing to your server IP.
  • In CyberPanel, go to "SSL" -> "MailServer SSL."
  • Select your domain (yourdomain.com). CyberPanel will attempt to issue SSL for mail.yourdomain.com.
  • Restart Postfix/Dovecot if prompted or from Server Status -> Services Status.

• Check CyberPanel Logs: Look in /home/cyberpanel/error-logs or website-specific logs.
• Check OpenLiteSpeed Logs: /usr/local/lsws/logs/error.log and stderr.log.

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ https://%{SERVER_NAME}%{REQUEST_URI} [R=301,L]

• Select Package: Choose a pre-defined package (e.g., Default) or create one under "Packages." This sets resource limits
• Select Owner: Usually admin or the user you are logged in as
• Domain Name: Enter your full domain name (e.g., yournewsite.com)
• Email: Enter an admin email address for the site
• Select PHP: Choose the desired PHP version for this site (e.g., PHP 7.4, 8.0, 8.1)

• SSL: Check this if your DNS is already pointing and you want to issue Let's Encrypt SSL immediately. If DNS isn't ready, you can do this later (Topic 12)
• DKIM Support: Check this to enable DKIM for email on this domain
• open_basedir Protection: Check for enhanced security (restricts PHP script access)
• Create Mail Domain: Check this if you plan to host emails for this domain on CyberPanel

• If DNS is already pointed and SSL was issued, try visiting https://yournewsite.com
• If DNS is not yet pointed, now is the time to go to your DNS provider (Cloudflare, Namecheap, etc.) and add A records for yournewsite.com and www.yournewsite.com pointing to your server IP

• All WordPress files (a .zip archive is best)
• A .sql export of your WordPress database

• Using File Manager:
  • In CyberPanel, go to "Websites" -> "List Websites" -> "Manage" for your site -> "File Manager"
  • Navigate to the public_html directory
  • Delete any default files (like index.html) if present
  • Click "Upload," select your WordPress .zip file, and upload it
  • Once uploaded, select the .zip file and click "Extract." Extract to public_html
• Using FTP:
  • Create an FTP account in CyberPanel ("FTP" -> "Create FTP Account")
  • Connect to your server using an FTP client (FileZilla) with the FTP credentials
  • Navigate to the public_html directory
  • Upload your unzipped WordPress files here

• Follow Topic 22: "How to Create and Manage Databases in CyberPanel." Note the database name, username, and password

• In CyberPanel, go to "Databases" -> "phpMyAdmin"
• Select your newly created database from the left sidebar in phpMyAdmin
• Click the "Import" tab
• Click "Choose File," select your .sql database backup file
• Ensure character set is utf8mb4 (usually default)
• Click "Go" (or "Import")

• In CyberPanel File Manager (or via FTP), locate and edit the wp-config.php file in your public_html directory
• Update the following lines with your CyberPanel database details:

  define( 'DB_NAME', 'your_cyberpanel_db_name' );
  define( 'DB_USER', 'your_cyberpanel_db_user' );
  define( 'DB_PASSWORD', 'your_cyberpanel_db_password' );
  define( 'DB_HOST', 'localhost' ); // Usually localhost

  

• This is crucial. You might need to use a tool like "Velvet Blues Update URLs" plugin after logging into WordPress, or directly update siteurl and home options in the wp_options table via phpMyAdmin if you can't log in

• Access File Manager:
  • Log in to CyberPanel
  • Go to "Websites" -> "List Websites"
  • Click "Manage" for the desired website
  • Click the "File Manager" button
• Navigating:
  • You'll typically land in the website's home directory (e.g., /home/yourdomain.com)
  • The website's public files are in public_html. Double-click to enter folders
• Common Operations:
  • Upload Files: Click the "Upload" button, select files, or drag-and-drop
  • Create Folder/File: Click "New Folder" or "New File"
  • Edit File: Select a file, click "Edit." A text editor will open
  • Copy/Move: Select file(s)/folder(s), click "Copy" or "Cut," navigate to the destination, click "Paste"
  • Delete: Select file(s)/folder(s), click "Delete." Confirm
  • Permissions (CHMOD): Select a file/folder, click "Permissions." Set numeric values or check boxes
  • Extract Archive: Upload a .zip (or other supported archive), select it, click "Extract"
  • Compress (Create Archive): Select files/folders, click "Compress." Choose archive type and name

• An FTP client installed on your computer (e.g., FileZilla, Cyberduck)

• Create an FTP Account in CyberPanel:
  • Log in to CyberPanel
  • Go to "FTP" -> "Create FTP Account"
  • Select the website (domain)
  • Enter a username (e.g., myftpuser)
  • Enter a strong password
  • Set the path (usually defaults to the website's home directory, or you can set it to public_html)
  • Click "Create FTP"
• Configure Your FTP Client (e.g., FileZilla):
  • Open FileZilla
  • Host: Your server's IP address or your domain name (if DNS is pointed)
  • Username: The full FTP username (e.g., myftpuser@yourdomain.com or just myftpuser - CyberPanel will clarify this on the FTP list page)
  • Password: The FTP password you created
  • Port: 21 (standard FTP). For SFTP (more secure, if enabled on server), use port 22
  • Click "Quickconnect" or save it in Site Manager
• Transferring Files:
  • The left pane in FileZilla is your local computer; the right pane is your server
  • Navigate to public_html on the server side
  • Drag and drop files/folders between panes to upload or download

• Create a phpinfo.php file in your website's public_html directory with the content:
• Access yourdomain.com/phpinfo.php in your browser. The displayed PHP version should match what you selected
• Important: Delete the phpinfo.php file after verifying for security reasons

• If you need specific PHP extensions for the selected version:
  • Go to "Server" -> "PHP" -> "Install PHP Extensions" (or "Manage PHP Extensions")
  • Select the PHP version you're using for the site
  • Install or uninstall extensions as needed

• Select Website: Choose the website you want to back up. You can select "ALL" to back up all websites
• Select Destination:
  • Local: Backups will be stored on the same server (in /home/backup/)
  • Remote (SFTP/FTP): Requires server IP/hostname, port, username, password, and remote path
  • Amazon S3: Requires Access Key, Secret Key, Bucket Name, and Region
• Frequency:
  • Daily: Specify the time (HH:MM) for the daily backup
  • Weekly: Specify the day of the week and time
• Retention: Specify how many recent backups to retain (older ones will be deleted automatically)

• List Backups: Go to "Backup" -> "List Backups" to see completed backups
• Restore Backup: Select a backup and click "Restore"
• Download Backup: Option to download backup files

• Monitor disk space for local backups
• For better disaster recovery, use remote backup destinations
• Periodically test restoring backups to verify they work

• Go to "Websites" -> "List Websites" -> "Manage"
• Check for LiteSpeed Cache section/toggle

• Access OpenLiteSpeed WebAdmin at http://:7080
• Navigate to Virtual Hosts -> your vhost -> Cache tab
• Ensure "Enable Cache" is set to "Yes"

• Enable caching in "LiteSpeed Cache" -> "Cache" tab
• Configure guest mode for optimal caching

• Image Optimization (WebP generation)
• CSS/JS minification and combination
• Database optimization
• CDN integration

• Access Logs: Record all requests made to your website (visitor IPs, pages visited, user agents).
• Error Logs: Record errors generated by your website scripts (PHP errors, etc.) or the web server.

• Log in to CyberPanel.
• For a specific website:
  • Go to "Websites" -> "List Websites."
  • Click "Manage" for the desired website.
  • Look for a "Logs" or "Error Log" / "Access Log" section or button.
• You might see options to view "Access Logs" and "Error Logs" directly in the browser or download them.
• For OpenLiteSpeed Server Logs (more general):
  • Go to "Server Status" -> "LiteSpeed Status" -> "View Error Log" / "View Access Log" (these are often server-wide, not site-specific).
  • Alternatively, logs are often found via command line at /usr/local/lsws/logs/ (e.g., error.log, access.log, stderr.log).

• Error Logs: PHP errors (fatal errors, warnings, notices), 404 errors not found by the site, permission issues.
• Access Logs: Suspicious activity, traffic patterns, popular content.

• Dashboard Overview: The main CyberPanel dashboard usually displays widgets for current CPU, Memory, and Disk usage.
• Server Status:
  • Go to "Server Status" -> "Resource Usage" (or similar, name might vary slightly).
  • This section often provides more detailed graphs or real-time updates for CPU, Memory, Disk I/O, and Network Traffic over time.
• LiteSpeed Status:
  • Go to "Server Status" -> "LiteSpeed Status."
  • This shows current connections, LiteSpeed processes, and other web server-specific metrics.

• High CPU: Could indicate inefficient scripts, high traffic, or insufficient server power.
• High Memory: Large applications, memory leaks in scripts, or too many processes.
• Low Disk Space: Affects website operation, email, backups.
• High Bandwidth: High traffic, large file downloads.

• top or htop (for real-time process and resource monitoring).
• df -h (for disk space).
• free -m (for memory usage).
• 

• Select Website: Choose the website this database will be associated with from the dropdown. This usually prefixes the database name and username.
• Database Name: Enter a name for your database (e.g., mydb, wp_db). CyberPanel will typically prefix it (e.g., yourdomain_mydb).
• Database Username: Enter a username for accessing this database (e.g., myuser). CyberPanel will also prefix this.
• Password: Create a strong password or use the "Generate" button. Store this password securely.

• Go to "Databases" -> "List Databases."
• Select a website to see its associated databases.

• In the "List Databases" view, you can usually find an option to "Change Password" for a database user.

• In the "List Databases" view, there's an option to "Delete" a database. Be careful, this is irreversible!

• phpMyAdmin is a web-based tool for managing MySQL database content (running queries, importing/exporting data, managing tables).
• In CyberPanel, go to "Databases" -> "phpMyAdmin."
• This will usually auto-login you to phpMyAdmin if accessed from the panel for a site you manage, or it might present a login screen where you use the database username and password you created.

• Select Package: Choose a package
• Select Owner: Usually admin
• Domain Name: Enter the full subdomain name (e.g., blog.yourdomain.com)
• Email: Admin email
• Select PHP: Choose PHP version
• Check SSL, DKIM, etc. as needed

• Type the domain name you want to park (e.g., myotherdomain.com)

• Issue SSL for the alias domain
• The alias domain should appear as an option in the SSL certificate for the main domain
• Re-issue the SSL to cover both domains

• cPanel Server IP Address: The IP of your old cPanel server.
• Username: Your cPanel username.
• Password: Your cPanel password (or API token if that method is supported).
• Security: Choose SSH or WHM API. SSH is common.

• There might be options for what to migrate (files, databases, emails). Usually, you'd migrate all.

• Website files are in the correct public_html for each migrated domain.
• Databases are created and data is present (check via phpMyAdmin).
• Email accounts are created (if email was migrated).
• DNS records for the migrated domains will need to be updated.
• Test the websites thoroughly.
• Issue SSL certificates for the domains on CyberPanel.

• Taking full cPanel backups (.tar.gz files).
• Transferring them to the CyberPanel server.
• Manually creating websites in CyberPanel.
• Manually extracting files to public_html.
• Manually creating databases and importing SQL data.
• Manually creating email accounts.

• Cause A: Incorrect URL/Port: You must use https://:8090.
  • Solution: Double-check you're using https://, the correct server IP, and port 8090.
• Cause B: CyberPanel Service Not Running: The lscpd service might be down.
  • Solution (via SSH):
    1. Log in to your server via SSH
    2. Check status: systemctl status lscpd
    3. If not active, start it: systemctl start lscpd
    4. Enable it to start on boot: systemctl enable lscpd
    
• Cause C: Firewall Blocking Port 8090: Your server's firewall might be blocking port 8090.
  • Solution: Ensure port 8090 (TCP) is open in your firewall configuration.
    • For CSF (if installed): Check /etc/csf/csf.conf for TCP_IN, add 8090 if missing, then csf -r
    • For firewalld: firewall-cmd --permanent --add-port=8090/tcp, then firewall-cmd --reload
    
• Cause D: IP Address Changed: If your server's IP changed.
  • Solution: Verify your server's current IP address.

• Cause A: Incorrect Credentials: Simple typo or forgotten password.
  • Solution: Carefully re-type username (usually admin) and password.
• Cause B: Forgotten Admin Password:
  • Solution (via SSH):
    1. Log in to server via SSH
    2. Run the password reset command:
       For CyberPanel versions 1.7.1 and above:
       adminPass
       For older versions:
       cd /usr/bin/
python anitPass.py --password
    

• Cause: Multiple incorrect login attempts might trigger fail2ban or CSF to ban your IP.
• Solution:
  • Wait for the ban to expire (e.g., 10-30 minutes)
  • If you have SSH access, you can unban your IP:
    • CSF: csf -dr then csf -ra
    • Fail2ban: Identify the jail (e.g., cyberpanel) and use fail2ban-client unban
  • Whitelist your IP if it's static

• Cause: If the server disk is full, services including CyberPanel might fail.
• Solution (via SSH): Check disk space with df -h. Free up space by deleting old backups, logs, or unnecessary files.

• Explanation: When you update DNS records, these changes need to be communicated from your authoritative DNS server to other DNS resolvers across the internet. This process can take anywhere from a few minutes to 48-72 hours.

• Explanation: Every DNS record has a TTL value that tells resolvers how long to cache the record before checking for updates.
• Action: When planning DNS changes, lower the TTL a day in advance (e.g., to 300 seconds) to speed up propagation.

• Explanation: Your devices cache DNS lookups and might still have the old IP address.
• Solution:
  • Flush DNS cache:
    • Windows: ipconfig /flushdns
    • macOS: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
    • Linux: sudo systemd-resolve --flush-caches or sudo /etc/init.d/nscd restart
  • Reboot your router
  • Change to public DNS (8.8.8.8, 1.1.1.1)

• Explanation: Browsers cache DNS information.
• Solution: Clear browser cache or use incognito mode.

• Explanation: Typos in DNS records or wrong record types.
• Solution: Double-check all DNS records at your provider.

• Explanation: Changes won't work if you're editing DNS at the wrong provider.
• Solution: Verify nameserver settings at your domain registrar.

• Explanation: Your DNS provider might be experiencing problems.
• Solution: Check provider's status page.

• DNSChecker.org
• whatsmydns.net

• MX Records:
  • Check: Do they point to your CyberPanel server's hostname?
  • Tool: Use an MX lookup tool (e.g., mxtoolbox.com).
• A Record for Mail Hostname: Does mail.yourdomain.com have an A record pointing to your server's IP?
• SPF Record: Is it present and correct for your domain?
• DKIM Record: Is it set up in CyberPanel ("Email" -> "DKIM Manager") and published in DNS?
• DMARC Record: Is it present?

• Check: Are Postfix (SMTP) and Dovecot (IMAP/POP3) running?
• How: In CyberPanel, go to "Server Status" -> "Services Status."
• Via SSH: systemctl status postfix, systemctl status dovecot

• Check: Does mail.yourdomain.com have a valid SSL certificate?
• How: In CyberPanel, "SSL" -> "MailServer SSL." Issue/reissue if needed.

• Check: Are standard email ports open in your server's firewall?
  • 25 (SMTP)
  • 465 (SMTPS)
  • 587 (SMTP Submission)
  • 110 (POP3)
  • 995 (POP3S)
  • 143 (IMAP)
  • 993 (IMAPS)
  

• Check: Correct server names, ports, usernames, passwords, and SSL/TLS settings.

• Check: Has the email account exceeded its disk quota?

• Check: Is the server out of disk space?
• How: df -h via SSH or CyberPanel dashboard.

• Check: Has your server's IP been blacklisted?

• Check: Does your server IP have a valid rDNS record?

• Check: Examine mail server logs for specific error messages.
• Location (via SSH): Often /var/log/mail.log or /var/log/maillog.

• Check if you've hit sending limits with external services.

• Send a test email to check-auth@verifier.port25.com or use mail-tester.com.