@Michiel Tack Thanks for doing this. I think you will probably have to submit your letter as a manuscript – although you might want to double check that. Technical info for submissions to the journal here: https://www.editorialmanager.com/jobm/default.aspx I would recommend getting an ORCHID ID if you have not already got one, as this is a generic ID which is needed to submit a manuscript to any science journal. Not all journals require ORCHID for letters though, and some ask you to register with their own systems too. Be prepared that it may take a couple of hours to get the IDs and fill in all the necessary forms. If you’d like me to have a look at the letter, or need any other advice, please feel free to copy me in on any private conversations.