I saw some threads and discussions about people looking to add custom information to a message but did not find the information I was looking for.
I want to optionally "tag" E-Mails with a CustomerID and/or a TransactionID.
I tried the Notes Zimlet which is quite nice but realized that the information is not searchable which means no hook from a customer ID to the messages with the same customer ID.

After some more approaches I found the API command SetCustomMetadata which allows to add metadata to the messages.
I added:

<meta section="UDX_Data">
<a n="CustomerID">10000</a>
<a n="TransactionID">456123</a>

Which is about what I was trying to do but still not searchable.
As we have quite a lot of transactions and customers it seems not practicable to me to use the built in tags for this issue.

I got the hint to use conversation IDs to tag my transactions the other way round which would work but is more a workaround not a solution.

Has anyone an idea or hint which could lead to a soulution?