Hi JCHUK,
Since you're having difficulty sending emails on your iPhone, we recommend that you try the steps in the link below.
If you can’t send emails on your iPhone or iPad – Apple Support (UK)
To perform the steps in the article we suggested above, click and open the link, read the subheadings below, and try each step.
1) Before you begin
2) Check the Outbox for unsent email
3) Check your email address and password
4) Contact your email provider or system administrator
5) Remove your email account and set it up again
We recommend the steps above because they will show you what to do if you're unable to send emails on your device.
If the steps in this article haven't helped, contact your email service provider for more information.
Thanks for using the Apple Support Communities.
Cheers!