This account is controlled by the MassMessage extension. Any user with the "massmessage" user right (list) can send messages via Special:MassMessage which are delivered using this account. Messages may also be sent via Meta-Wiki.
A hidden comment in the wikitext source of the text added indicates who actually sent the message, what wiki they sent it from, and what input list was used. Mass message events are logged.
If you do not wish to receive any messages, add your user talk page to Category:Wikipedians who opt out of message delivery. You do that by adding the following line to anywhere on your talk page:
[[Category:Wikipedians who opt out of message delivery]]
All further questions about mass messaging should be made on the mass message senders page, not on this account's talk page.