In-Reply-To processing is broken - header not being parsed correctly

Summary

Replying to a JIRA issue email without the issue key in the subject results in a new ticket being created as the 'In-Reply-To' value is not being parsed correctly.

Environment

Cloud
Server

Steps to Reproduce

1. Send an email to JIRA
2. Forward the confirmation email to another email address
3. Remove the issue key from the subject line and reply to all

Expected Results

JIRA should parse the 'In-Reply-To' line within the message header and match it to the existing ticket

Actual Results

JIRA opens a new ticket

What is seen is that the current versions of JIRA Server generates email notifications with mail headers such as:

Message-ID: <398968471.2.1431682003072.JavaMail.andy@dev-jira>
In-Reply-To: <JIRA.12400.1431681970000@Atlassian.JIRA>
References: <JIRA.12400.1431681970000@Atlassian.JIRA> <JIRA.12400.1431681970299@dev-jira>

When a reply is sent the headers are included, and used by the standard JIRA mail handlers (amongst others)

MailThreadManager

however, in the method:

private Issue parseIssueFromMessageId(final String messageId)

An example In-Reply-To header value of:

<JIRA.12400.1431681970000@Atlassian.JIRA>

Is split based on . into:

[<JIRA, 12400, 1431681970000@Atlassian, JIRA>]

The method above tries to parse [2] which is '1431681970000@Atlassian' into a Long which throws a RuntimeException.

Workaround

Ensure that the issue key is referenced in the subject line of the email