A suppression list is a record of emails to whom you do not want to send campaigns. The suppression is applied by choosing the list/lists under the suppress list section when on the new campaign page.
List types: In Maropost, you can either create a normal list or create a suppression list. While creating the list, you will see "Normal" and "suppressed" options in the dropdown of "List Type" section.
If we choose the list type as "Suppressed", then the list will not appear in the normal list section on the campaign creation page, it will only appear under the "suppress lists" section on the campaign creation page. If you choose it as a "Normal" list type, then it will appear under normal list type section as well as under the suppress list option.
The suppression list is to suppress the contacts while sending the campaign. In case you have the list of contacts to whom you do not want to send the campaign and there is a possibility that the same contacts are present in the sending list, then you can select the respective list of the contacts to whom you do not want to send the campaign in the "suppress lists" section and the contact will get suppressed.
So let's say jane@maropost is present in the list "A" to which you are sending the campaign and you have selected the list "B" in the suppress lists section in which the contact jane@maropost is also present, the contact jane@maropost will not receive the campaign and will get suppressed.
1. Only the contacts who are present as "Subscribed" in the list being used as a suppression list, will not be sent emails. The contacts with the status "Unsubscribed" are not affected.
2. Suppression will only work in normal campaigns, not for the test campaigns**