All Google products in China have been severely disrupted since June of this year and Chinese users have not been able to access Gmail via its web interface since the summer. However, email protocols such as IMAP, SMTP and POP3 had been accessible but are not anymore. These protocols are used in the default email app on iPhone, Microsoft Outlook on PC and many more email clients.
On December 26, GFW started to block large numbers of IP addresses used by Gmail. These IP addresses are used by IMAP/SMTP/POP3. Chinese users now have no way of accessing Gmail behind the GFW. Before, they could still send or receive emails via email clients even though Gmail's web interface was not accessible.
Google's own traffic chart shows a sharp decline of Chinese traffic to Gmail.
Below is a ping request to the Gmail SMTP server, which is completely inaccessible in China.
Chinese users now have absolutely no way of using Gmail, except through the use of circumvention tools. GFW started to partially disrupt Gmail years ago with periodical disruptions and throttling to make it look as if Gmail servers were unstable. Then GFW blocked all Google websites in June 2014. Now GFW has blocked email client access to Gmail. I believe cutting Gmail/Google off in one stroke would draw too much attention, even in China. So GFW has been cutting Google services gradually and has now finally completed the grand mission of completely eliminating Google's presence in China.