in the universal email wizard, click the To button to go to the advanced to screen and Increase the Wait Between sending emails option.
I'm having a similar problem with clients receiving duplicate emails. I'm sending about 250 emails via looped option using a SQL table of email addresses. Each address receives two emails. I changed my timing settings to this:
$BurstSize = 25;
$BurstTime = 1;
$WaitTime = 2;
It used to be 50,1,1 respectively. Also, either setting seems to work ok with short email lists. Help. Thanks. Files attached.