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the ‘via’ part gives the clue. Its values are defined in CustomerRequestChannelSource 
:
“via Email” is used by JEMHC
“via Jira” is used by:
the Issue Collector , if used
direct REST calls from external scripts using the standard Jira REST API of nnn.atlassian.net/rest/api/2/issue (secured with a user token)
“via API” is used by:
direct REST calls from external scripts using the standard JSM REST API of http://nnn.atlassian.net/rest/servicedeskapi/request (secured with a user token)
“via Portal” appears to be for portal users..
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