There are a lot of Wikimedians, including newbies, from mainland China who complained that they can't receive emails from Wikimedia, including email address verification and notification. Also, they reported emails from Wikimedia's mailing lists (lists.wikimedia.org) are occasionally dropped. The Wikimedians suffering from this issue are all using email service from Tencent, a Chinese internet giant. After googling for this problem, I found that Tencent's email service will reject all emails from an IP address when the amount of emails that IP sent reaches a certain number. Those rejected emails will neither be delivered to the inbox, even nor the spam folder. One way to get through the limitation is by purchasing services like Mailgun, or by directly contact a Tencent's staff who work for their email service to whitelist the domain name and IPs manually.
Now, I managed to get contact with a Tencent's stuff, and he would like to whitelist Wikimedia's IPs. I can get Wikimedia's IPs by simply looking through WMF's Autonomy system, but they need a narrower range.