I use `org-export` to generate my end of week email reports. Once of the links I have in those reports is mu4e. I have a helper function to translate them into something more useful:

    ;; Exporting
    (defvar my-org-mu4e-index-links
      (rx
       (: (or "query:i:" "msgid:") (group-n 1 (one-or-more any))))
      "A regex to match mu4e links of the form:

        query:i:20170228171921.21602-1-ale+[email protected]
    ")

    (defun my-org-mu4e-export (path desc format)
      "Format mu4e links for export."
      (when (string-match my-org-mu4e-index-links path)
        (cond
         ((eq format 'html)
          (format "<a href=\"%s%s\">%s</a>"
                  "https://www.google.com/search?q="
                  (match-string 1 path)
                  desc))
         ((eq format 'jira)
          (format "[%s|%s%s]"
                  desc
                  "https://www.google.com/search?q="
                  (match-string 1 path)))
         ((eq format 'ascii)
          (format "%s\nMessage-Id: <%s>" desc (match-string 1 path))))))

    (use-package ox
      :config
      (org-link-set-parameters "mu4e" :export 'my-org-mu4e-export))

However what I really want is what happens with other links where the link text is surrounded by `[]` and the link is displayed at the bottom of the section. e.g.:

    Task 1
    ======

      - posted message [about foo] to mailing list

    [foo] Message-Id: <bar>
    
However I've not been able to work out where in the exporter transcoders and filters this is done. I assume I should be able to set some sort of parameter for mu4e style links to deal do this.