I don't want to compicate the diagnosis - I have tried this also before with PHP 8.1 and had the same trouble. Either way, I am using the latest mailparse extension.
System => Linux uvdesk.journalroot.local 5.10.0-23-amd64 #1 SMP Debian 5.10.179-1 (2023-05-12) x86_64
Build Date => Feb 22 2023 20:07:47
Server API => Command Line Interface
Virtual Directory Support => disabled
Configuration File (php.ini) Path => /etc/php/7.4/cli
Loaded Configuration File => /etc/php/7.4/cli/php.ini
Scan this dir for additional .ini files => /etc/php/7.4/cli/conf.d
Additional .ini files parsed => /etc/php/7.4/cli/conf.d/10-mysqlnd.ini,
/etc/php/7.4/cli/conf.d/10-opcache.ini,
/etc/php/7.4/cli/conf.d/10-pdo.ini,
/etc/php/7.4/cli/conf.d/15-xml.ini,
/etc/php/7.4/cli/conf.d/20-bcmath.ini,
/etc/php/7.4/cli/conf.d/20-calendar.ini,
/etc/php/7.4/cli/conf.d/20-ctype.ini,
/etc/php/7.4/cli/conf.d/20-curl.ini,
/etc/php/7.4/cli/conf.d/20-dom.ini,
/etc/php/7.4/cli/conf.d/20-exif.ini,
/etc/php/7.4/cli/conf.d/20-ffi.ini,
/etc/php/7.4/cli/conf.d/20-fileinfo.ini,
/etc/php/7.4/cli/conf.d/20-ftp.ini,
/etc/php/7.4/cli/conf.d/20-gd.ini,
/etc/php/7.4/cli/conf.d/20-gettext.ini,
/etc/php/7.4/cli/conf.d/20-iconv.ini,
/etc/php/7.4/cli/conf.d/20-imap.ini,
/etc/php/7.4/cli/conf.d/20-intl.ini,
/etc/php/7.4/cli/conf.d/20-json.ini,
/etc/php/7.4/cli/conf.d/20-mbstring.ini,
/etc/php/7.4/cli/conf.d/20-mysqli.ini,
/etc/php/7.4/cli/conf.d/20-pdo_mysql.ini,
/etc/php/7.4/cli/conf.d/20-phar.ini,
/etc/php/7.4/cli/conf.d/20-posix.ini,
/etc/php/7.4/cli/conf.d/20-readline.ini,
/etc/php/7.4/cli/conf.d/20-shmop.ini,
/etc/php/7.4/cli/conf.d/20-simplexml.ini,
/etc/php/7.4/cli/conf.d/20-sockets.ini,
/etc/php/7.4/cli/conf.d/20-sysvmsg.ini,
/etc/php/7.4/cli/conf.d/20-sysvsem.ini,
/etc/php/7.4/cli/conf.d/20-sysvshm.ini,
/etc/php/7.4/cli/conf.d/20-tokenizer.ini,
/etc/php/7.4/cli/conf.d/20-xmlreader.ini,
/etc/php/7.4/cli/conf.d/20-xmlwriter.ini,
/etc/php/7.4/cli/conf.d/20-xsl.ini,
/etc/php/7.4/cli/conf.d/20-zip.ini,
/etc/php/7.4/cli/conf.d/25-mailparse.ini
php -ini
curl
cURL support => enabled
cURL Information => 7.74.0
Age => 7
Features
AsynchDNS => Yes
CharConv => No
Debug => No
imap
IMAP c-Client Version => 2007f
SSL Support => enabled
Kerberos Support => enabled
Directive => Local Value => Master Value
imap.enable_insecure_rsh => Off => Off
mailparse
mailparse support => enabled
Extension Version => 3.1.4
Directive => Local Value => Master Value
mailparse.def_charset => us-ascii => us-ascii
mbstring
Multibyte Support => enabled
Multibyte string engine => libmbfl
HTTP input encoding translation => disabled
libmbfl version => 1.3.2
mbstring extension makes use of "streamable kanji code filter and converter", which is distributed under the GNU Lesser General Public License version 2.1.
Multibyte (japanese) regex support => enabled
Multibyte regex (oniguruma) version => 6.9.6
Directive => Local Value => Master Value
mbstring.detect_order => no value => no value
mbstring.encoding_translation => Off => Off
mbstring.func_overload => 0 => 0
mbstring.http_input => no value => no value
mbstring.http_output => no value => no value
mbstring.http_output_conv_mimetypes => ^(text/|application/xhtml+xml) => ^(text/|application/xhtml+xml)
mbstring.internal_encoding => no value => no value
mbstring.language => neutral => neutral
mbstring.regex_retry_limit => 1000000 => 1000000
mbstring.regex_stack_limit => 100000 => 100000
mbstring.strict_detection => Off => Off
mbstring.substitute_character => no value => no value
but should arrive.