Mail can be received, but it cannot be sent. What's going on here?

This should be the setting problem of the sending server. The complete setting method is as follows, please modify it.

Methods/steps

Before setting QQ mailbox on iPhone, you need to confirm the setting information of QQ mailbox. Please log in to your QQ mailbox first, and click the "Settings" option on the page.

Then click "Account" in the mailbox setting interface, as shown below.

Then please find the column "POP3/IMAP/SMTP/Exchange/carddav/caldav service" on the account page to confirm whether all the following services have been started. As shown in the figure below, none of my current services are enabled, so I need to click the "Open" function.

If you have enabled these services of QQ email, then we can set up email on iPhone. Open the Settings app on the existing iPhone, as shown in the figure.

Find the column "Mail, Address Book, Calendar" in the settings list, and click Enter.

Then please click "Add Account" under the ledger, as shown in the figure.

Then please click on the column of QQ mailbox, as shown in the figure below.

Then please enter the email name in the name column, and you can enter it at will. Then enter the QQ email address, such as 12345678@QQ.com, then enter the password, and finally click the "Next" button.

When the mailbox is verified, you can click the "Save" button.

When you return to the mailing list, you can already see the QQ mailbox.

Next, after we open the email application, we can also see the QQ mailbox and send and receive emails.