I just upgraded Ubuntu on my server to 16.04. Went to send a campaign and everything worked fine, except it didn’t send. It would send a test message though. I am on phplist 3.0.6. When I click on process queue, it very quickly says it was sent, but I never see statics and I never receive any message.
Checked log and nothing showing after sending. When I checked campaigns, it showed the campaign as still active.
Since you updated the os, I would recommend that you upgrade phpList to the lastest version, too, that would eliminate any issues that have already been addressed.
Note that your php version > 5.2.x
Should be using PHP 5.4 according to settings. Would like to, but also running an older version of Joomula for that site too and need to upgrade that also.
Still getting the problem, although one test message did make it through.