Hello Nir,
sorry for the late reply. I had no time.
The abuse stopped. I don't know if you managed to change something yourself, if my own measures had an effect (I geo-banned his area for some time) or if the person got bored by doing his "joke".
(He wrote me he's having "a little fun" with me)
However I thought the message is send out by the system, not the client and I use Nicotine+.
So if it happens again, I'll get in contact with the Nicotine+ guys seeing what they can do about it, but I'll let you know here. Maybe I just need to update to the latest Nicotine+ version which I am not very keen of doing as once I did so, the Nicotine+ config file got completely damaged and I had to do "it" all over again, like making a new user list.
greets, and many thanks for decades of great Soulseek. :)