Our client uses an Outlook plugin that attaches a 1 pixel x 1 pixel containing XML code for filing against project work. For some time now, instead of inserting the attachment, it's being attached, we don't run custom policies and this is not happening for the client's signature.
The vendor's response is lackluster and all they ask you to do is refer to technical support and compare an Outlook client that does not have the issue to one that does, unfortunately, we cannot find one that is not experiencing the issue. This occurs on new emails and replies to emails. We have Outlook 365 & Outlook 2016 in the environment both exhibit the same issue.
This is a problem because the recipient receiving the email thinks there is an attachment waiting for them, opens it and due to the 1x1 pixel size they see nothing and assume something is wrong.
I've found plenty of information around stopping the embedding of images but nothing really addressing the reverse, also use different mail editors e.g. rich text vs html - this made no difference.
We do not use any other plugin's other than the one mentioned. Any insights to this issue would be greatly appreciated.