Why does the SMTP server create a new campaign each time you send an email?

If you want to avoid having the SMTP server create a new campaign every time you send out emails, you must add the appropriate GUID on the headers of the email. 
Look for the following GUID: campaign_guid: your-campaign-id-here

This is the ID of your campaign, whose statistics will be recorded for every transactional email sent through our SMTP service.

If you don't use the above GUID on the header of the email, a new campaign is always created based on the subject of the email you sent out. 

You can check the other GUID available for you to use when sending out campaigns via our SMTP service.