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Non-JIRA email users don't need to have an account created to interact with JIRA remotely. JEMH can store remote user emails in a TEXT(unlim) custom field, referred in the Profile Email section, see Enable non JIRA -Jira Account holders to receive issue updates and create/comment on Issues for details.
Alternatively, non-JIRA email users can have an account created in JIRA but not be granted 'right to use', this then allows a degree of management via permissions associated to groups, e.g. 'email-users'.
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