Corrupted record in index cache file

Symptoms

Dovecot generates errors similar to the following in the /var/log/maillog file:

dovecot: imap(user@domain.tld)<782><R+lKIYC32qB/AAAB>: Error: Corrupted record in index cache file /home/user/mail/domain.tld/user/dovecot.index.cache: UID 1001: Broken physical size in mailbox INBOX: read(/home/user/mail/domain.tld/user/cur/1509799350.M592274P32540.server.hostname.tld,S=314477,W=318606:2,S) failed: Cached message size larger than expected (314477 > 2305, box=INBOX, UID=7137)

dovecot[50907]: imap(user@domain.tld)<1459255><FgOsXW8/IIIAAAAAAAAAAAAAAAAAAAAB>: Error: Mailbox INBOX: Index /home/user/mail/domain.tld/user/dovecot.index: index not found via open(): Lost log for seq=1 offset=0: Missing middle file seq=1 (between 1..4294967295, we have seqs 114,115): .log.2 contains file_seq=114 (initial_mapped=0) - fscking (reopen_reason: Index not open)

The account may also not be able to sync with email clients such as Roundcube or Outlook.

Description 

This is often caused by the Dovecot index for the user or the referenced file being corrupted.

Workaround

1. Verify if the file contains valid data:

   cat /home/user/mail/domain.tld/user/cur/1509799350.M592274P32540.server.hostname.tld,S=314477,W=318606:2,S

2. If it does not, delete the file or move it to a different directory, otherwise continue.
3. Remove the index for the user so that it will be rebuilt:

   /scripts/remove_dovecot_index_files --user user

If the issue persists, you may want to consider installing cPanel SOLR for better indexing on the server.

Additional Resources

What is the cpanelsolr process?

How to install cPanel Solr in WHM