Sina mailbox does not open pop3 and smtp protocols by default. Pop3 and smtp are both transport protocols, but they are both protocols about mail transmission. The former stands for receiving mail, and the latter stands for sending mail. Each of them has his own server and, of course, his own address.
Not being open doesn't mean it can't be used, because the web version doesn't need these to send and receive emails.
Also pay attention to the port number of Sina pop3 and whether SSL is used.
Open the POP3 and SMTP protocols as follows:
1. Log in to Sina email.
2. Find the Settings button
3. Click "More Settings"
4. Account
5. Continue to drop down the webpage, and sure enough, the pop3 and smtp service settings we are looking for appear below. By default, it is displayed as off.
6. Click Open
7. You need to fill in the verification code to save the settings, which is also for safety, so don't bother.
8. Successfully saved the settings. At this time, if you need to add a Sina email account on the mobile terminal, it will be very smooth.