As discovered today with the Wikidata weekly summaries run, MassMessage ignores the namespace if it is a interwiki link.
Example; {{#target:Wikidata:Status updates|www.wikidata.org}}
The message gets delivered to https://wikidata.org/wiki/Status_updates which then errors due to it being in NS_MAIN and not NS_PROJECT which was specified.
Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=58524