How to fix dovecot.index: modseq_hdr.log_offset too large
You need to remove broken index files.
Try to use cPanel script:
/scripts/remove_dovecot_index_files --user USERNAME
If doesn’t work remove them manually
find . -type f -name "dovecot.index*" -exec rm -fv {} \;
System then re-generate them again… Read the rest