    Starting with RT 5.0.0, the minimum supported MySQL version is 5.7.7
    because this is the first version to provide full support for 4 byte
    utf8 characters in tables and indexes. Read on for details on this
    change.

    Starting with RT version 5.0.4, MySQL 8 is also supported.

    RT 5.0.0 now defaults MySQL tables to utf8mb4, which is available in
    versions before 5.7.7. However, before MySQL version 5.7.7, utf8mb4
    tables could not have indexes with type VARCHAR(255): the default size
    for index entries was 767 bytes, which is enough for 255 chars stored
    as at most 3 chars (the utf8 format), but not as 4 bytes (utf8mb4).
    5.7.7 sets the default index size to 3072 for InnoDB tables, resolving
    that issue.

    https://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-7.html#mysqld-5-7-7-feature

    In MySQL, RT uses the utf8mb4 character set to support all
    unicode characters, including the ones that are encoded with 4 bytes in
    utf8 (some Kanji characters and a good number of emojis). The DB tables
    and the RT are both set to this character set.

    If your MySQL database is used only for RT, you can consider
    setting the default character set to utf8mb4. This will
    ensure that backups and other database access outside of RT have the
    correct character set.

    This is done by adding the following lines to the MySQL configuration:

    [mysqld]
    character-set-server = utf8mb4

    [client]
    default-character-set = utf8mb4

    You can check the values your server is using by running this command:

        mysqladmin variables | grep -i character_set

    Setting the default is particularly important for mysqldump, to avoid
    backups to be silently corrupted.

    If the MySQL DB is shared with other applications and the default
    character set cannot be set to utf8mb4, the command to backup the
    database can be set explicitly:

        ( mysqldump --default-character-set=utf8mb4 rt5 --tables sessions --no-data --single-transaction; \
          mysqldump --default-character-set=utf8mb4 rt5 --ignore-table rt5.sessions --single-transaction ) \
            | gzip > rt-`date +%Y%m%d`.sql.gz

    Restoring a backup is done the usual way, since the character set for
    all tables is set to utf8mb4, there is no further need to tell MySQL
    about it:

        gunzip -c rt-20191125.sql.gz | mysql -uroot -p rt5

    These character set updates now allow RT on MySQL to accept and store 4-byte
    characters like emojis. However, searches can still be inconsistent. You may be
    able to get different or better results by experimenting with different collation
    settings. For more information:

    https://stackoverflow.com/a/41148052
    https://dev.mysql.com/doc/refman/5.7/en/charset-unicode-sets.html