Historically, until version 2.0, when you wanted to send a campaign to more than one list/segment, MailWizz would merge the selected lists/segments into a new list and would then send the campaign to that new list.
Performance wise, this is a very bad idea, because you end up duplicating a lot of data.
This also means MailWizz would have to search in a lot of data, which means slower application overall.
When we implemented this functionality, it was the only viable option given the requirements at that time.
However, once we started working on MailWizz 2.0, we had enough time to do something about this problem, in a way that is also backward compatible, and our solution is called Sending Groups.
With the arrival of MailWizz 2.0, when you create a campaign, you can add it into a Sending Group.
You can add multiple campaigns in a Sending Group, each campaign targeting a different list and/or segment.
When MailWizz sends a campaign that is part of a Sending Group, for each email address that is targeted in the campaign,
MailWizz does a lookup to see if that email address received any other campaign that is part of the same Sending Group.
If it finds the email address during the lookup, then MailWizz marks the campaign for that email address as sent, and moves on.
If it does not find the email address during the lookup, then MailWizz will send the campaign to that email address and then move on.
This allows for great flexibility with a minimum performance cost.
Not only you can send campaigns to as many lists and segments as needed without worrying that email addresses
that are part of multiple lists will get duplicate campaigns, but you can also modify each copy of the campaign
and change its attributes, like subject, content, etc, so you can test the inboxing rate.
Another benefit is that you can add a campaign into a sending group at any time, even weeks or months after your initial send out to a Sending Group.
The Sending Groups feature is very powerful and it can help you target subscribers in ways that was not possible in MailWizz 1.x.
As with anything in MailWizz, we advise using this feature only if you really need it and you are sure it is going to help.