Login wecom exmail with your wecom account qr scanning.
Go to 邮箱绑定 and generate a client password for your SMTP purpose
If you don't have this option, meaning you did not binding this mail to wechat yet. It is compulsory to binding wecom with wechat to use smtp. You can binding it at the wecom app, at Setting(设置) 》 Account & Security (账户与安全) 》 Wechat
