Email body encoded as Content-Transfer-Encoding: base64 added as duplicate attachment

Summary of Issue

When JIRA Service Desk Mail Handler processes an email where the body of the email is encoded as Content-Transfer-Encoding: base64:

1. For a new ticket - the decoded contents are added into Ticket Description (but HTML is also added as an attachment to the ticket)
2. For an existing ticket - the decoded contents are added into Ticket Comment (but HTML is also added as an attachment to the ticket)

The behaviour works as expected (no additional attachment) when email body is encoded as Content-Transfer-Encoding: quoted-printable.

How to reproduce

1. Send an email to the JIRA Service Desk listening email address
2. Once the email has arrived and processed by JIRA Service Desk
   • Extract out the contents of AO_2C4E5C_MAILITEMCHUNK and decode
   • Update the main body encoding from Content-Transfer-Encoding: quoted-printable to Content-Transfer-Encoding: base64
   • Also encode the actual email body to base64
   • Re-encode the whole email as base64
   • Re-update into AO_2C4E5C_MAILITEMCHUNK and set AO_2C4E5C_MAILITEM.status to 'NEW' for reprocessing

Expected Result

Email body updated into Ticket Description / Ticket Comment without adding it again as an attachment.

Actual Result

In JIRA Service Desk (for both Server and Cloud):

1. For a new ticket - the decoded contents are added into Ticket Description (but HTML is also added as an attachment to the ticket)
2. For an existing ticket - the decoded contents are added into Ticket Comment (but HTML is also added as an attachment to the ticket)

Workaround

There is no usability issue as the comment is posted into the ticket appropriately but the redundant attachment is occupying additional disk space.

The work around would be to simply delete the attachment (which has a random 8 character name such as ohecJTek)