Hello, I am using the mail merge add on to Thunderbird to send to up to about 500 recipients maximum, each with an individual personalised email. I am using the "send later" option in mail merge so that I can check for typos etc. in the outgoing messages before they go. My ISP, not unreasonably, doesn't allow more than about 15-20 messages per 5 minutes to be sent via their SMTP servers, in an attempt to stop spam and server overload. So, I'd like to limit the sending rate of messages in the outbox to no more than say one every 30 seconds. I've looked but can't see any settings to achieve this, or any add-ons. I'm happy to leave my PC on for the time it will take to send the messages. Anyone know how to do this?