+Unless their system blocks unsolicited "mentions", the person tagged will likely receive a "Mention" post/activity or become a direct participant in the conversation in the case of public posts.
+Friendica blocks incoming “mentions” from people with no relationship to you.
+The exception is an ongoing conversation started from a contact of both you and the 3rd person or a conversation in a forum where you are a member of.
+This is a spam prevention measure.
+
+Remote mentions are delivered using the OStatus protocol.
+This protocol is used by Friendica and GNU Social and several other systems like Mastodon, but is not currently implemented in Diaspora.
+As the OStatus protocol allows this Friendica user can be @-mentioned by users from platforms using this protocol in conversations if the "Enable OStatus support" is activated on the Friendica node.
+These @-mentions wont be blocked, even if there is no relationship between the sender and the receiver of the message.