well from this article i found on google [article](https://hostpapasupport.com/error-503-valid-rcpt-command-must-precede-data-apple-mail/#:~:text=The%20%E2%80%9CError%20503%3A%20Valid%20RCPT,authenticated%20by%20your%20email%20server.) it says that smtp error 503 is caused by 2 things
* The first is that your email server requires you to check your email (I don't know what that means but i assume it's an authentication issue like @Isofruit explained above) * The second is that your email provider does not support smtp so check if you can get an application key from your mail provider and check if your mail provider supports smtp
