Cannot reply to emails message says incorrect password but I can send and receive

Hey there peterbrattley,

I understand that you are experiencing an issue with your mail account on your iPhone. Here is an article for you with some troubleshooting steps that can help you address this issue:

Follow these steps first:

1. To make sure that you're connected to the Internet, open Safari and go to www.apple.com.
2. Log in to your email provider's website and make sure that the account is active and that you're using the right password.
3. Check your email settings.
4. Restart your iOS device.
5. Remove the affected email account from your device with these steps:
   1. Tap Settings > Mail, Contacts, Calendars.
   2. Tap the email account.
   3. Tap Delete Account.
   4. Add your account again.

Get help with Mail on iPhone, iPad, and iPod touch - Apple Support

https://support.apple.com/en-us/HT201419

Thanks for coming to the Apple Support Communities!