transaction code vs 'x-mimiaid' header

[hassansin]

When sending transactional email, I get a response of transaction code like s-1558. Does this code has any particular format? I'm asking because I need to use this code to find out the actual email from our database of emails. I noticed when I receive the email, it has a header x-mimiaid which looks similar to the above transaction code but not exactly equal (1558-xxxxxxxxx-xxxxxxxxxx-e66c71cefda3f4f8ed980be1ab62466b0c41920f). Does anyone knows about the exact format of transaction code?