What happened?

1. Users groups are set as
   [Root group with no users]
   - [sub group 1 with users]
   - [sub group 2 with no users]
   - [sub group 2.1 with users]

2. In back office, go to Users > Mass Mail Users

3. Set a mail subject

4. Set a mail content (simple text)

5. Mass Mail Users settings :
   "Mail to Child User Groups" => Enabled
   "Send in HTML Mode" => Disabled
   "Send to Blocked Users" => Disabled
   "Recipients as BCC" => Enabled
   "Group" => Select [Root group with no users]

6. Send mail

7. Mass Mail Users says "xx mail are sent"

Version

5.4.3

Expected result

Bulk emails must be received without error.

Actual result

• No email was received
• The error message "Mail delivery failed: returning message to sender" is returned to super-admin email address with this type of content

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

test@mail.com
message has lines too long for transport

System Information

No response

Additional Comments

No response