This is a system account. This account is used by the MassMessage extension (help for this extension is available at mw:Help:Extension:MassMessage) to the MediaWiki software (in a manner similar to a bot) to send messages to user's talk pages and to project pages.
If you would like to opt out of receiving messages via MassMessage, add your user talk page to Categoria:Opted-out of message delivery.
Leaving messages on this account's talkpage is useless, because this account is not operated by any human being (human beings use either Special:MassMessage or meta:Special:MassMessage and do not see messages on this account's talkpage). If any problems arise, please post them in the Vicipaedia:Taberna.