We take many steps to ensure that addresses are not added fraudulently or maliciously to customer accounts.
If an email address at a major domain is submitted to your list, and the "user" part of the email address (the part before the @ symbol) is four characters or fewer, that subscriber will need to confirm.
In most cases, extremely short user names in the most popular domains are either mistypes, blatantly bogus, or dead email addresses.
All of those can negatively affect your deliverability. So, in order to prevent them from being fraudulently or maliciously subscribed to your list, they will need to confirm.
How Do We Determine "Popular" Domains?
We look at email addresses adding to lists by filling out web forms. We take the most commonly submitted domains and base this on that list. The list is recalculated daily based on the previous day's signups.
Domains that will frequently be on the list include: