Since my last posting I have done some further investigation into the issue that I am experiencing with the site that I work with and thought I would post some further information that may be of help to others.

When sending out the newsletter I had been letting the default setting remain to send one email per user that is found in the advanced setting area.  That places the users email address in the 'to' line of the email header and gives an introduction to the user with their user name before the contents of the newsletter begins in the body of the email.  So it does add a nice personal touch to the message but the price is that it is one email per user it is being sent to which can cause problems with hosting provider limits.

If you change the default setting in the advanced setting area of the newsletter screen to use the 'bcc' mode, then only one email message is sent out, the address you use in the header section of the newsletter is the address that shows up in the 'to' line of the email, and in the body of the email message the newsletter contents appear without any sort of personalized introductory greeting for the user.  Since it is only one email message being sent then it should help overcome some limits that may be in place by a hosting provider. 

Regarding your comments about how nice it would be to have some configurable settings to 'throttle' the rate at which the individual emails were sent out as a possible way of not running into exceeding limits of a hosting provider, that may be a hard order to fill.  A lot of it would have to deal with what limits are in place at a particular hosting provider meaning are those limits in terms of number of messages sent in one 'session' or are they in terms of hours or even in terms of how many messages can be sent in a days time.  I do like the idea but it does present somewhat of an implementation problem.

Anyway, I am just sharing information and thoughts that I have had since my last posting on the matter.