Archive mail by year and month with dovecot, see https://tkaefer.de/blog/2022/01/04/archive-mail-by-year-and-month-with-dovecot/

mail-archive.sh

#!/bin/bash
 
USER="email@example.com"
 
# The path in dovecote mail folder to put the subfolders to
ARCHIVE_ROOT="INBOX.Archives"
 
# The paths of the folders to be processed during archive
BOXES_TO_ARCHIVE=("INBOX.Archive" "Archive*")
 
# Define from what - relatine to now - date in the past the archiving should be started
# use date "-d '...' " notation
# eg for initial imports this could be set to "-20 year"
ARCHIVE_START_DATE="-3 month"
 
# Define until which - relative to now - date mails should be archived, mails younger that date that date are omitted
# use date "-d '...' " notation
RETENTION="-1 month"
 
# Check if coreutils date is present in Alpine Linux
# "-/+ x month" operations in date are not supported in busybox date implementation
# Therefore coreutils date is required
date '+%Y-%m-%d' -d "+1 month"
if [ $? -ne 0 ]; then
  # Install coreutils in Alpine Linux
  apk add --no-cache coreutils
fi
 
date '+%Y-%m-%d' -d "+1 month"
if [ $? -ne 0 ]; then
  # install failed
  echo "installing coreutils date failed - exiting"
  exit 1
fi
 
# Search for all existing subfolders in BOXES_TO_ARCHIVE
BOXES=()
IFS=$'\n'
for BOX in ${BOXES_TO_ARCHIVE[@]}; do
    BOXES+=($(doveadm mailbox list -u ${USER} ${BOX}))
done
 
ENDDATE=$(date '+%s' -d "${RETENTION}")
isodateiter="$(date '+%Y-%m-%d' -d "${ARCHIVE_START_DATE}")"
 
while [[ $(date +%s -d $isodateiter) -le $ENDDATE ]]; do
  YEAR="${isodateiter:0:4}"
  MONTH="${isodateiter:5:2}"
 
  SINCE="${YEAR}-${MONTH}-01"
  BEFORE="$(date '+%Y-%m-%d' -d "$isodateiter +1 month")"
 
  for BOX in ${BOXES[@]}; do
    # echo "# Check if there is anything to archive in BOX ${BOX} for period between BEFORE and SINCE"
    # echo "doveadm search -u ${USER} MAILBOX ${BOX} SENTBEFORE ${BEFORE} SENTSINCE ${SINCE} | wc -l"
    # Check if there is anything to archive in BOX ${BOX} for period between BEFORE and SINCE
    echo "checking for mails in ${BOX} SINCE ${SINCE} AND BEFORE ${BEFORE}"
    if [ $(doveadm search -u ${USER} MAILBOX ${BOX} SENTBEFORE ${BEFORE} SENTSINCE ${SINCE}  | wc -l) -gt 0 ]; then
      # Create and subscribe ARCHIVE subfolder if it doesn't exist
      # echo "# Create and subscribe ARCHIVE subfolder if it doesn't exist"
      ARCHIVE="${ARCHIVE_ROOT}.${YEAR}.${MONTH}"
      doveadm mailbox status -u ${USER} messages ${ARCHIVE} >/dev/null 2>&1
      if [ $? -ne 0 ]; then
        echo "creating new ARCHIVE Folder ${ARCHIVE}"
        doveadm mailbox create -u ${USER} ${ARCHIVE}
        doveadm mailbox subscribe -u ${USER} ${ARCHIVE}
      fi
      # Move the mails to ARCHIVE subfolder
      # echo "# Move the mails to ARCHIVE subfolder"
      echo "Move mails to ARCHIVE folder ${ARCHIVE}"
      doveadm move -u ${USER} ${ARCHIVE} mailbox ${BOX} SENTSINCE ${SINCE} SENTBEFORE ${BEFORE}
    fi
  done
 
 
  isodateiter="${BEFORE}"
done