we encounter a strange problem with phpList 3.3.1: It doesn't send all emails, but only parts of the recipients. It's always a different amount of emails, that isn't sent, in total numbers and percent of the entire list.
One list was 10,692, and 2,291 were not sent, and in another list there were 4,499, and 128 were not sent. The messages remain in the queue of unsent messages, and if we try to send the remaining, it seems to work, but actually does nothing.
It's not a problem with the blacklisted recipients, as they rare already taken out.
I would be happy for any advice!