Then go to your Netease mailbox, click Settings → Basic Settings → Signature Settings → Add Signature in the upper right corner, and paste the picture you just copied into the edit box to save.

When writing a letter, there is a "signature" menu in the toolbar of the email editing interface. Click the drop-down menu to select the signature you want to use.

(Note: If the paste source online picture is invalid, the signed picture will not be able to display O(∩_∩)O~).