Relaying of photos not allowed

I have no problem sending photos via email with iOS 8.4.

Check with your email provider to see what the problem may be.

And as previously stated, the information you provided points to an issue with your email provider. check with them.

PS: there is a difference between sending an email that contains only text and sending one with a sizable file attachment.

Did you send the 2 mail (text only and text+photo) to the same recipient? Did you fill out your username and password in your outgoing SMTP server settings?

This issue usually happens when you try to send an email from your normal email provider using cellular data instead of Wi-Fi. The recipients email provider sees the incoming email as one that has been "relayed" through more than one server. Scammers and spammers use this technique to hid their identity and that your recipients email provider has blocked the message. Try sending it again when you are at home.

Ralph9430 wrote:

This issue usually happens when you try to send an email from your normal email provider using cellular data instead of Wi-Fi. The recipients email provider sees the incoming email as one that has been "relayed" through more than one server. Scammers and spammers use this technique to hid their identity and that your recipients email provider has blocked the message. Try sending it again when you are at home.

No, it isn't the recipient's mail server that rejects the email. It's the sender's (Harry Newton) mail server which refuses to send out the email without authenticating to the (outgoing) SMTP server.

Spammers use misconfigured SMTP servers (open relay) that do not require authentication to send out spam.