Question: I am having an issue with the "Send Email" button on order view pages within the Magento admin panel. I am having this issue on two separate installations of Magento ver. 1.8.1.0 on four servers, so I am assuming it as a bug at this point. I just installed a completely fresh version and tested it again with the same issue.

I have gone as far as installing a fresh copy of 1.7 side by side with 1.8.1. 1.7 sends that particular email just fine, 1.8.1 does not.

Has anyone else experienced this or have any suggestions for a debug process?

Answer: 
Just been looking into this myself. I've followed the code and functions back to this function "public function sendNewOrderEmail()" in:

app/code/core/Mage/Sales/Model/Order.php

starting at line 1270 is the following code:

```
$emailSentAttributeValue = $this->load($this->getId())->getData('email_sent');
    $this->setEmailSent((bool)$emailSentAttributeValue);
    if ($this->getEmailSent()) {
        return $this;
    }

```

This is checking the sales\_flat\_order db table to see if the email has already been sent to the customer and if so just to return, but this does not send the email and should throw an error. So I would say it is a bug somewhere.
To fix it so you can resend order/invoice emails etc..

Copy

app/code/core/Mage/Sales/Model/Order.php

to

app/code/local/Mage/Sales/Model/Order.php

and comment out line 1273

```
if ($this->getEmailSent()) {
            //return $this;
        }

```

Works a charm for me. But literally only this second tested it.

Tested using ver. 1.8.1
I was having the same issue with fresh installs of 1.8, 1.8.1 and even 1.9. My solution for now since it doesn't seem to be acknowledged as a bug yet was to just back up to 1.7.2. Hopefully this bug gets fixed so we can upgrade.