How to fix gzip-compressed Maildir messages after cPanel import

[isscbta]

In some cases, after running

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v-import-cpanel-backup

on myVesta, email messages imported from cPanel may remain gzip-compressed inside the Maildir structure. When that happens, Dovecot and the mail stack may not read those messages properly, which can result in missing or broken inbox contents.

In /var/log/dovecot.log you may see something like this:

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Mar 23 15:21:07 imap([email protected])<3347150><yUjivrFNXJt/AAAB>: Error: Mailbox INBOX: UID=1: read(/home/user/mail/domain.com/account/cur/1748433712.M456713P1942205.someserver,S=80724,W=82092:2,S) failed: Cached message size larger than expected (80724 > 19442, box=INBOX, UID=1) (read reason=mail stream)
Mar 23 15:21:07 imap([email protected])<3347150><yUjivrFNXJt/AAAB>: Error: Mailbox INBOX: Deleting corrupted cache record uid=1: UID 1: Broken physical size in mailbox INBOX: read(/home/user/mail/domain.com/account/cur/1748433712.M456713P1942205.someserver,S=80724,W=82092:2,S) failed: Cached message size larger than expected (80724 > 19442, box=INBOX, UID=1)
Mar 23 15:21:07 imap([email protected])<3347150><yUjivrFNXJt/AAAB>: Error: Mailbox INBOX: UID=1: read(/home/user/mail/domain.com/account/cur/1748433712.M456713P1942205.someserver,S=80724,W=82092:2,S) failed: Cached message size larger than expected (80724 > 19442, box=INBOX, UID=1)
Mar 23 15:21:07 imap([email protected])<3347150><yUjivrFNXJt/AAAB>: Info: FETCH failed: Internal error occurred. Refer to server log for more information. [2026-03-23 15:21:07] in=337 out=1273 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0

The procedure below safely detects gzip-compressed mail files, decompresses them in place while preserving timestamps, removes Dovecot index files, and then restarts Dovecot so indexes can be rebuilt correctly.

Important:

• Run this only after confirming that imported mail files are actually gzip-compressed.
• Make sure to replace

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  /home/user/mail/

  with the correct mail path for the affected account.
• It is strongly recommended to create a backup before making any changes.

Step 1, go to the mail directory

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cd /home/user/mail/

Step 2, detect and decompress gzip-compressed Maildir files

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find ./ -type f -exec sh -c '
  for f; do
    if file "$f" | grep -q "gzip compressed data"; then
      tmp=$(mktemp) || exit 1

      if gunzip -c "$f" > "$tmp"; then
        touch -r "$f" "$tmp" && mv "$tmp" "$f"
      else
        rm -f "$tmp"
      fi
    fi
  done
' sh {} +

What this does:

• scans all files under the selected mail directory
• checks whether a file is gzip-compressed
• decompresses the file into a temporary file
• preserves the original timestamp
• replaces the original compressed file with the decompressed version

Step 3, remove Dovecot index files

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find \( -name "dovecot.index" -or -name "dovecot.index.cache" -or -name "dovecot.index.log" -or -name "dovecot.index.log.2" -or -name "dovecot.mailbox.log" -or -name "dovecot.index.log.newlock" \) -delete

Why this is needed:
Dovecot may still keep old mailbox index information. Deleting these index files forces Dovecot to rebuild them based on the now-correct message files.

Step 4, restart Dovecot

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systemctl restart dovecot

Result

After this procedure, the imported Maildir messages should be readable normally, and the mailbox indexes should be rebuilt correctly.