If your client has web hosting services, chances are that they have access to a mail list program already as part of the services.
Bcc is OK for a few people on the list but sending to hundreds is only going to get your host blackholed as a spammer and anyone else who relies on email on that web host will suddenly find themselves in a situation where no one can communicate. I had a situation back in 2009 where I sent an email to a local government news service who then blackholed the server and Yahoo wanted $20 for unblocking my email from their black list (this is one way Yahoo makes money) and was duly pointed to the authority that blocked who then had a triad about the legal issues of blocking a political party who was registered with the electoral commission and that what they had done and how they conduct their business.
Never seen so much back tracking in my life.
So be warned, if your server gets black holed, you will have a hard time getting it de-listed unless you want to pay the company email regs which if memory serves me, a sister company to Yahoo.
It is not about your server sending the emails out, it is about who receives your email and how that recipients email client classifies your email and if they are linked to an email blackhole service.