We use Profit Mail but we cannot send attachments as we get a 404 error

We use Profit Mail but we cannot send attachments as we get a 404 error.

If you're referring to this account: kelmorkustoms,  that the account's Privacy Setting has been set to "Enabled". It means that the attachments can only be viewed if you are logged on to the said account, otherwise, it will return a 404 error as you mentioned.

Please try disabling it by going to the account's settings and uncheck the following options:

Here's a quick guide for that: