Rated 5 out of 5 stars

Works smoothly and accurately. Some messages may not be defined as dupes because of the Compare Size option. Playing aroung with settings makes good result to avoid wrong removing!

Hey Eyal,

Sorry for my previous review :)
Do you plan further extention development?
Why there are duplicate messages which look absolutely the same, but one of them has the size =0 Which one I should consider to keep?

Thanks!

This review is for a previous version of the add-on (0.3.12). 

The extension supports a wide customizable range of comparison criteria; the messages you want to define as dupes are (almost certainly) actually different somehow: Different second of arrival; extra newline; different order of recipieints; etc.

It is actually a safety feature that, by default, the comparison is very strict. I'm sure you'll agree it's better to fail to delete some dupes, by mistake, than to delete non-dupes, by mistake. When you set the appropriate criteria you get the result you want.