ナレッジベース

Overview

Users may encounter an IMAP internal error when attempting to access webmail. This issue typically occurs when the Dovecot dovecot.index.cache file for a specific mailbox exceeds the default virtual memory size limit (vsz_limit) configured for the IMAP service. The following guide outlines how to identify affected mailboxes and adjust the configuration to resolve the out-of-memory error.

Symptoms

When logging into webmail, users receive the following error message:

IMAP error reported by server

INTERNAL ERROR
Could not load message from server

Concurrently, the system log at /var/log/maillog records an out-of-memory fatal error for the Dovecot IMAP service:

Feb 10 06:41:40 www0 dovecot: service=imap, user=user@example.com, ip=[203.0.113.1]. Fatal: master: service(imap): child 10671 returned error 83 (Out of memory (service imap { vsz_limit=512 MB }, you may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)

Diagnosis

The default vsz_limit for the IMAP service is set to 512 MB. If a user's index cache file exceeds this threshold, the IMAP process terminates with error code 83. In some cases, files such as /var/qmail/mailnames/example.com/user/Maildir/dovecot.index.cache may grow significantly beyond this limit.

To identify mailboxes with oversized cache files, execute the following command:

find /var/qmail/mailnames/ -type f -name dovecot.index.cache  -exec ls -al {} \; | sort -k 5 -n  

This command lists all dovecot.index.cache files sorted by size in ascending order. Record the largest file size to determine the appropriate new memory limit.

Resolution

1. Create or edit the custom configuration file at /etc/dovecot/conf.d/zzz_custom.conf.
2. Add the service imap block and set the vsz_limit parameter to a value higher than the largest cache file identified during diagnosis. For example:

service imap {
vsz_limit = 1024MB
}

3. Save the configuration file.
4. Restart the Dovecot service to apply the changes:

systemctl restart dovecot

Troubleshooting & Common Issues

• Configuration Syntax Errors: Ensure proper indentation and syntax within /etc/dovecot/conf.d/zzz_custom.conf. Incorrect formatting may prevent Dovecot from starting. Verify the configuration using standard Dovecot validation commands before restarting if issues persist.
• Persistent Memory Limits: If users continue to experience out-of-memory errors after increasing the limit, monitor mailbox growth and consider implementing automated cache maintenance or storage quota policies.
• Service Restart Failures: Confirm that no other Dovecot configuration files conflict with the custom settings. Check system logs for additional error details if the service fails to start successfully.