[exim] Why "blackhole"?

Hi list,

I recently discovered this very curiously message in the mainlog:

2018-02-28 00:56:11 1eqp6G-0004wp-IR DKIM: d=email.microsoftemail.com
s=102420140131 c=relaxed/relaxed a=rsa-sha1 b=1024 [verification
succeeded]
2018-02-28 00:56:12 1eqp6G-0004wp-IR LMS check accept: 250 OK
2018-02-28 00:56:12 1eqp6G-0004wp-IR <=
bounce-866153_HTML-528534629-5439879-228974-247@???
H=(mta28.email.microsoftemail.com) [66.231.92.214] P=esmtps
X=TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256 S=69286
id=df627243-be0d-4776-9939-7408baf52a86@???
2018-02-28 00:56:12 1eqp6G-0004wp-IR => blackhole (local_scan
discarded recipients)
2018-02-28 00:56:12 1eqp6G-0004wp-IR Completed

I really can't understand why the E-Mail will be discarded.
Can someone help me?

Thanks
Luca Bertoncello
(lucabert@???)