I finally found the way. To obtain the ID, it is required to launch the "run query" action first. In the action fields, set the email address in the email field and the clean Message ID in the query field. Do not select any other option, nor fill any other field. In the response you should see another ID base64 like format. This is the ID used to operate emails. Keep in mind that this ID changes everytime you perform any action over the email (moving it to a different folder for instance). Hope this helps.
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