Hi @KunoE ,
To build off of what Zoe said, if you're doing a Resend to New Contacts, and any of your "new" uploads are contacts that have already received the email, then the system won't send to those other contacts. If you've deleted and re-added any contacts that were already sent the email in the past, then the system simply wouldn't send it to them, but after awhile it's possible that all the new contacts added were in fact already part of that list / sendout.
The main way get around this would be to at the very least copy a master template you've created, and send that as a new email to your list(s). Another potential option is to do a Quicksend of the email (assuming you're sending to less than 500 at a time), which will override the built-in send history restrictions of the Resend to New Contacts method.
If you don't believe this to be the situation, and neither of the workarounds suggested work for your needs, please reply directly to the @ mention email you receive from this reply with your username, the name of the list(s) being sent to, and the name of the email being sent. Or you can also call our general support for live, 1:1 assistance troubleshooting as well.
See also:
Resending overview
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