Qq mailbox shows that the sender's security verification failed. What should I do?

1. Verification failed due to network reasons. You can try sending the verification code again.

2. Because the filtering rule is set in the recipient's mailbox, the mail is blocked. You can try to change the recipient's mailbox settings.

E-mail is considered as spam because it is sent too frequently. You can try to reduce the sending frequency and resend the verification code.