Dear Mrs X,
I'm writing to enquire about jobs opportunities within your company.
I am available from July and am interested in any customer-service jobs you may have. I have attached my CV, if you have any questions please don't hesitate to contact me and I look forward to hearing from you.
(I would write 1-2 sentences briefly outlining why you'd be good for these types of jobs as people don't always bother to open the attachments)
Yours sincerely, (is more common in letters rather than an email)