Mail @ Issue (Send email to issue)

Mail @ Issue (Send email to issue) is JIRA Cloud plugin. It gives you possibility to attach emails as comments. Just forward your message to: my_company+issue@jira.email

Every issue will have unique email address. Forwarded email will be visible in issue 'Emails' tab.

JQL

You can search for issue by mail content using JQL: issue.property[mail].body ~ "my query"