StarMail is a plugin that is used mainly in roleplaying. However, the features of this plugin would be useful for our server as we can utilise them in a different way.
The benefit of StarMail is that you can send packages to people - these packages can contain items that OPs want to give other OPs. It's useful when your friend is offline but you want to leave an item for them before you go off for the day.
The link to the plugin is here:
https://www.spigotmc.org/resources/star-mail.73406/