Just a final thing on this.
On my host, with a script timeout of 60 seconds, i can squeeze out nearly 200 emails before failure
I can just about live with this limit, but my client says that sometimes only 15 or 20 emails get through on their host.
They are understandable frustrated and are considering setting up with another hosting provider, but I am reluctant to suggest mine, (fatcow) who are generally excellent, but obviously restrictive.
I just checked their php ini with their current hosting provider and execution time is set to 30 seconds - i will take a look at setting the time limit on page.
With shared hosting, is this exacerbated ?