We do not allow a list to have duplicate addresses. However your list member could receive multiple copies of your campaign if one of the following situations occurs:
- Your list member signed up with two different emails and has set an automatic forwarding to one of the email addresses.
- You sent your campaign multiple times, targeted to different categories of your list, and that list member happens to belong to multiple categories.
Our system only ever sends out one copy of your campaign to each list member. If the list member's server is having any delivery issues we will retry and deliver the campaign again. If we did not do this, it would take longer to deliver campaigns because we would be waiting on slower servers to respond.
Unless a list member's system reports back with a bounce message or an acknowledgment of delivery, any email system, including ours, would interpret the lack of response as an intermittent delivery failure and retry delivery. If the list member's server has this issue, or is in anyway set up incorrectly, it is possible that they may see multiple copies of a campaign.
We recommend that you ask your list member to check their email server setup to see if there are any such issues.