my mail says sender address invalud. why

Hello Wilkshake,

Thanks for reaching out to the Apple Support Communities. We understand you are looking for some help with sending emails on your iPhone. We are happy to help provide some guidance.

Are you currently signed in with your Apple ID if you go into Settings? It should show you your name and Apple ID at the top of the Settings window if you are. Also make sure that your iPhone has a good internet connection when trying to send an email.

Take a look at the steps outlined in the following article that goes over what to do if you are encountering issues sending or receiving emails on your iPhone:

If you can’t send email on your iPhone, iPad, or iPod touch

Keep us updated on how it goes. We hope this information helps.

Cheers.