In foxmail, you only need to encrypt the contents and attachments of all outgoing emails and sign in Tools menu-System Settings-Security to cancel all outgoing emails.

Check SMTP settings again.

Select "Mail Server" in the menu-Mailbox-Modify Mailbox Account Properties-Account Properties;

Check the space in front of the column "SMTP server needs authentication" on the right, click the next button "Settings"-"Authentication", select "Use the same information as pop3 server", and click "OK".