I’m running version 3.5.3 on a shared hosting besides WordPress using cron. Since the beginning I’m getting hourly (and sometimes 2 hours) report mails during the campaign, stating that the process had been terminated by another process. Processing continues and as all mails get sent nevertheless, so I did not consider this to be a massive problem.
As all else seemed to be running ok, I continued tweaking the sending speed (now batch processing is disabled) and switched on messagequeue_prepare. While in the beginning it took about 8 hours for about 4.000 mails, I got it down to 5 to 6 hours.
Today PHPlist is running for 17 hours and hasn’t finished yet, producing a lot of duplicates which results in recipients cancelling their subscription.
During the first campaigns, already some recipients reported getting the message several times, but that did stop after after the first tweaks in batch size and duration, so I suspected adjusting those settings might have been fixing that, too. But no. Today and weeks later about 50% of the recipients received 2-5 times the same message (according to the hosting provider).
There’s been one recipient it kept trying and trying. I suspended the campaign and marked it as sent. Now it does not show up in the list of sent messages. The campaign has been sent 9.628 times to 4.156 recipients.
Any idea what could be causing troubles like this?
Hosting also informed me, that there doesn’t seem to be smtp pipelining at work. This causes the script to wait for the recipient server to answer before sending the next command, which slows everything down, too. Is this a misconfiguration, a bug or by design?
And is it possible to speed up the sending by removing all variables from the message and tell the script to send batches of mails bcc to several recipients at once ? How so?