What we want to do now is extend the e-mail functionality: When creating a message, we can now enter:
Subject
Body
Attachment(s)
Recipient(s)

What we want to do is add any custom field, for now a time field where we can enter for example 7:30.

We want this value to be passed to for example a custom header in the e-mail: X-CRM-DURATION: 450 (in minutes).

OR we want this value, together with the Message-ID (so after sending), to be passed to any remote service we supply. This could be through SOAP or whatever else we could use.

We think we can achieve this by creating a Zimlet. However, when we look around on Google, we cannot find anything regarding the adding of fields, except for it being impossible.

Does anyone have an idea on how to achieve this? Or is it just not possible?

Thanks in advance.