You can use mentions to assign a user to a checklist item, or to inform other members of the team that the item is relevant to a user.
You can opt to Send email notifications for user mentions in the global settings.
Email notifications are not sent for self-mentions.
Anyone using the checklist can mention users. However, if you don't have Browse users and groups permission, then the user picker will only list assignee and reporter of the current issue (if they are set). No other users will be suggested.
Adding a mention
To mention a user type @ followed by part of the user's display name (full name) or nickname (username). A user picker will open. Select the appropriate user.
If the query is empty, i.e. the mention consist of "@" character only, the popup will show assignee and reporter for the current issue. You can also use "assignee" and "reporter" to find and mention the corresponding users.
Checklist stores mentions as the Atlassian account ID (a non-PII cryptic text like 557408:b0926d6a-bbb4-461e-a3e5-37858a82211d) of a user.
Mention by Email
You can also mention users by email addresses. The search will match partial emails for users who have made their email address public in their profile. Otherwise a full email address must be provided.
Mentioning by email can yield unexpected results. Searching with incomplete email addresses may show no user due to Jira limitations.
User Not Found
Mentions of non-existing (not found) users are displayed as plain text and not a highlighted lozenge.