Hi,
is it possible search a message by the message-id such I can do with Thunderbird? Could be important in some cases: I would also know if EMCLIENT permit to customize the search terms using the field in the header of the mail.
Thanks
Few months was passed and no answer to this question… 
No, it is not possible to search by message-ID.
Please click the advanced search option in the search box, where all the available search fields are listed.