Description

TL;DR: Ruby 3.1+ (even upgrading mail dependency to 2.8) breaks the plugin behavior.

Details:
Logstash 8.10+ versions use Ruby 3.1. Ruby 3.1 extracts bundled gems such as net-smtp, net-imap, etc.. dependencies. When running imap plugin with Logstash 8.10+ versions, we get LoadError: no such file to load -- net/smtp error.
In order to solve this error, mail dependency of this plugin needs to explicitly include net-smtp dependency which happened in mail-v2.8.
However, the big issue, when this plugin upgrades mail to 2.8+ (upgrade PR), plugin's behaviour is completely broken. The test cases show,

• email content type is null eligible
• attachments are automatically decoded

There is no workaround for now. We need more investigation and plan to bring this plugin to working state.