We have used our own scripts initially but eventually veered around to use Phplist for a client who had about 300,000 newsletters to send. We opted to buy a separate domain closely associated with the parent domain for this task. This was done specifically not to hurt the parent domain in case they slapped some ban on the main domain. Phplist is easy to administer for even non-technical client. There is a caveat - if you plan to send HTML mails observe the following:
In the body of the HTML mail, move the part inside the header (like the CSS , JS etc) into the body. Copy the portion only between the <body> and </body> into the Send message edit window (take care to press the Source button) excluding the <body> tags.
PHPlist - at least the version we used tended to strip out external CSS/JS/Image files. If you need to include image files in the body, use absolute reference.
I am sorry if I have stated the obvious - for a HTML Tutor.