CiviCRM Mailing does not set the Reply-To header to use VERP (CiviCRM return address) when Flexmailer is installed and using default option

CiviCRM Mailing does not set the Reply-To header to use VERP (CiviCRM return address) when Flexmailer is enabled and Traditional Mailing Handler using the default option of Automatic or CiviMail BAO or on page /civicrm/admin/flexmailer?reset=1

If the Traditional Mailing Handler option is set to Flexmailer Pipeline then the Reply-To header is set correctly.

This is problematic because all email replies are sent to the reply-to email address which is often a user mailbox and not processed by CiviCRM at all. The user receives all the bounced emails and out of office replies.

Because this problem occurs with the default options, there is a high likelihood that this problem will impact on a CiviCRM site.

Environment:

• CiviCRM 5.14.1
• Flexmailer extension 1.1.0
• Track replies using VERP in Reply-To header option is enabled
• Enable Custom Reply-To option is disabled

Agileware Ref: CIVICRM-1254