I got accepted to a PhD program in England. I received a formal offer letter on January 20th, which stated that I was supposed to contact the Graduate Studies Administrator via email in order to accept the offer. So I sent them an email on January 24th, telling them that I intended to accept it. However, I have not yet received their reply, and I am wondering if my email was properly delivered to them. According to the letter, the deadline to accept the offer is February 14th. Should I send them a follow-up email?