If the description in a linked JIRA issue contains an email address, the link is presented in the Stash/JIRA integration with the JIRA URI (http://host.domain.tld:8080/) pre-pended to the mailto: URL.

When the issue is viewed directly in JIRA, the mailto: is properly formed

To replicate,

• Create a JIRA issue with an email address in the description.
• Place the issue key in a commit,
• View integration link constructed in Stash.
• Click on the linked email address.