Zimbra Not Working: Simple Checks & Fixes Anyone Can Follow

If one found Zimbra not working or even not opening, then the reasons could be browser errors, DNS misconfiguration, etc. Recently, I’ve troubleshot these problems across multiple environments, and I’ve learned that appropriate fixes will resolve this Zimbra mail not working error. Today, I’ll share my experiences and solutions to resolve Zimbra issues step by step.

Common Reasons Why Zimbra Stops Working

As I said, we’ll learn everything step by step, so first learn why it occurs so you can easily prevent this in future: 

• Browser problems, i.e. cache, extensions, or an unsupported browser
• Incorrect DNS or MX records
• Mailbox service or backend failures
• Mail is stuck in the queue
• Full disk or storage failures
• IMAP Authentication Failed
• Server resource exhaustion, like CPU, RAM, or Java heap
• SSL certificate expiry
• Firewall or network blocks
• LDAP or authentication issues
• Sync errors on Outlook, Thunderbird, Android, or iOS

Identifying the root cause is the most essential thing to address the Zimbra issues.

Zimbra Not Working – Step-by-Step Fixes

Since there are many different reasons why this issue occurs, we need to follow specific troubleshooting steps for each one:

#1. Zimbra Webmail Not Working

If Zimbra Web Client doesn’t load or gets stuck on a blank screen, check the browser:

1. Clear browser cache and cookies
2. Try an alternate browser such as Chrome, Firefox, or Edge
3. Disable browser extensions like ad blockers or script blockers
4. Test Zimbra in Incognito Mode

If Zimbra loads correctly in incognito mode, the issue is related to extensions or cached data.

On the Zimbra server, run:

zmcontrol status

If any service is stopped, restart everything with:

zmcontrol restart

#2. Zimbra Login Not Working

Login issues are almost always related to:

• Wrong credentials
• Locked accounts
• LDAP failures

To fix the Zimbra not working:

• Verify if the username and domain are correct
• Reset the user password from the Admin Console
• Ensure the account is not disabled or expired

If Login Fails for All Users, this is mainly due to LDAP failures:

zmcontrol status

If LDAP is down:

zmldapstart

#3. Zimbra Shows Server Connection Error

Server Connection means the mailbox service (mailboxd) is not responding correctly. To address:

#1. Restart mailboxd:
zmmailboxdctl restart

#2. Check Java heap usage

Review logs:
/var/log/zimbra.log
/opt/zimbra/log/mailbox.log

If the logs show Out of Memory, then increase the Java heap allocation for quick results.

#4. Zimbra Mail Not Sending or Receiving

This is one of the most frequent Zimbra not working issues. The cause could be:

• DNS
• MTA failure
• mail queue backlog

So, for incoming Mail Issues, check:

• MX records
• Open ports (25, 110/995, 143/993)

MTA service:

zmmtactl restart

For Outgoing Mail Issues, verify:

• IP blacklist status

Postfix queue:
mailq

• TLS or SSL certificate status

If the queue is full:

postsuper -r ALL

#5. Zimbra Mobile Sync Not Working

IMAP folder is not properly syncing. Failures happen on:

• Outlook
• Thunderbird
• Android
• iOS

To resolve this, follow the set of instructions below:

• Re-check IMAP/POP/SMTP settings

Ensure IMAP/POP is enabled:
zmprov gs `zmhostname` | grep -i imap

• Ensure device time is correct
• Disable battery optimisation for the mail app

For Outlook using ZCO, recreate the profile or setup IMAP email on iPhone if the issue persists.

#6. Zimbra Not Working or Server Down

Critical outages are usually caused by:

• Full storage
• Corrupted databases
• Broken services

First Check

df -h

If storage is full, Zimbra will stop automatically. So, remove old logs, backups, or temporary files from /opt/zimbra/.

Restart Services:

zmcontrol stop
zmcontrol start

Check MariaDB (MySQL):

mysql.server status
mysql.server start

If mailbox databases show corruption, run:

/opt/zimbra/libexec/zmdbintegrityreport

#7. Zimbra SSL Certificate Errors

Expired or invalid certificates will block secure connections. So:
Check certificate expiry:

zmcertmgr viewdeployedcrt

Renew Let’s Encrypt certificates:

certbot renew

Deploy certificate:

zmcertmgr deploycr

After deployment, restart Zimbra services to see if the issue is resolved. 

#8. Zimbra Performance Issues

Slow performance is tied to:

• Low memory
• Heavy mailboxes
• Misconfigured Java heap

Optimisation Steps I Take:

• Raise Java heap size
• Enable mailbox cleanup for oversized accounts
• Add or increase swap space
• Tune MySQL configuration

#9. DNS Misconfiguration

If DNS records are wrong, Zimbra will fail to send or receive emails correctly.

Always verify:

• A record
• MX record
• SPF
• DKIM
• DMARC
• Reverse DNS (PTR)

How to Troubleshoot Zimbra Not Working – Quick Steps

Here are the quick step-by-step instructions to troubleshoot the issue in minutes:

#Step 1. Check Server Health

zmcontrol status

df -h
free -m

#Step 2. Test Webmail Access

Try different browsers, devices, and network connections.

#Step 3. Check Mail Flow

mailq
/var/log/zimbra.log

#Step 4. Validate DNS

dig mx domain.com

#Step 5. Restart Zimbra Services

zmcontrol restart

#Step 6. Review Logs

Check mailbox.log, zmmailboxd.out, and zimbra.log.

#Step 7. Adjust Server Configurations

Fix resource limits, DNS issues, or service failures.

#Step 8. Reboot as a Last Resort

Only after all other options fail.

How Does an Offline Backup Help When Zimbra Stops Working?

Above, we learned how to resolve the Zimbra Not Working issue, but what if you need to access mailbox data urgently, and you can’t even access it? The data is still on the server, but you can’t open Webmail or even download new emails until Zimbra is fully restored. Then, in that case, what will you do? 

Additionally, there is no quick method to resolve this issue, as we learned above. This is where an offline backup becomes useful.

If you already have a local copy of your Zimbra mailbox, you can still access your emails anytime, even when the server is unresponsive. For this purpose, I opt for the most reliable approach, i.e. SysTools IMAP Backup Tool, because I can’t afford to lose my data. 

It allows downloading the entire Zimbra mailbox through IMAP and storing it in common readable formats like PST, MBOX, EML, MSG, or PDF. Moreover, this utility works on both Windows and Mac OS. So, download this now for free, and ensure data continuity, even if you can’t access Zimbra. 

When to Contact Support?

Some Zimbra not working issues are too complex for basic troubleshooting, such as:

• Database corruption
• Broken upgrades
• Severe performance degradation
• Zimbra server not starting even after a restart

In such cases, I recommend taking help from an experienced Zimbra administrator or support consultant.

Author’s Verdict

With a structured troubleshooting approach, Zimbra Not Working can be solved quickly. Above, we discussed the same simply and clearly. Now, you have a proper knowledge of everything, that why it occurs, and how to resolve it. Additionally, it is suggested to export IMAP to PST, or any other desired format, to access data quickly, even if your service is not opening.

If you like this information, please share it with your friends, colleagues, or even bookmark this guide, which helps you to resolve this issue if it persists in future.