Using our new UI? You might want to check this help article instead.
All you have to do to avoid having the SMTP server create a new mailing list every time you send out emails is to add the appropriate guide on the headers of the email.
What you are looking for is the following guide:
- mailing_list_id: your_mailing_list_id :
This allows all the recipients to be added using the same mailing list ID.
If you don't use the above guide on the header of the email a new mailing list will be created based on the subject of the email you sent out.
Make sure to check the other guide which is available for you to use when sending out campaigns via our SMTP service.