Latest Fedora delivers version 2.120. Upstream released 3.001. When you have free time, please upgrade it. Also please consider enabling release monitoring <https://admin.fedoraproject.org/pkgdb/package/rpms/perl-Mail-Box/> to receive notifications about new versions automatically.
There is 3.002 version.
perl-Mail-Transport-3.000-2.fc26 perl-Mail-Box-3.002-1.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-fda53d1ef7
perl-Mail-Box-3.002-1.fc26, perl-Mail-Transport-3.000-2.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-fda53d1ef7
perl-Mail-Box-3.002-1.fc26, perl-Mail-Transport-3.000-2.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.