Currently we don't have a build in feature to mention groups and we already have a feature request raised for that end:
My suggestion is for you to vote for that feature request and add your thoughts in there so we can increase it's relevance.
As a work around you could use below third party plugin add on, which is free, and seems to enable that end:
Two vulnerabilities have been published for Confluence Server and Data Center recently: March 20, 2019 CVE-2019-3395 / CVE-2019-3396 April 17, 2019 CVE-2019-3398 The goal of this article is...
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