For some reason I think maybe due to my ISP I get a error when I mass email users.
I can trace via Mandrill who the last user was that received the mail but if emails are sent alphabetically is there anyway I can resume sending to the entire list?
As far as XF is concerned, there is no ability to resume an email operation.
If you have a large number of members and/or server or ISP limits, you may want to consider an external service.