Claws mails is one of those programs that if you take it at first impression, it doesn't seem that great. Those that take the time to investigate Claws Mail will find an absolutely incredibly powerful and ridiculously lightweight and fast power house of an email client. It takes just a couple steps and looking around and you'll find its awesome.

First the default theme, at this point I think they leave it that ugly just out of spite, lol. It's an easy fix though, there are many themes available for Claws-Mail. You can install theme individually or as a group either through Synaptic Package Manager or the terminal. To save time just open a terminal and enter the following:

sudo apt-get install claws-mail-themes

Once that is finished open Claws Mail, go to the configuration menu, select preferences then select themes on the left hand side. There should be a bunch of themes now available. Personally I always pick the 'Elementary' theme, because it fits the overall LXLE desktop nicely.

Claws Mail comes with many plugins preinstalled in LXLE. To enable the plugins to extend Claws functionality, simply go to the configurations menu and select plugins, you can then select what plugins you want to load. Once loaded with the right theme and your preferred plugins, you'll find Claws Mail is near impossible to beat.