The 'Send by email' function only works with locally installed email clients such as Microsoft Outlook and Mozilla Thunderbird. Other email clients may work if they support the simple MAPI protocol.
Internet email (where you use your internet browser to access email and not a local email program) is not supported. Of course you can still create your email messages and attach your invoices manually if you dont use a local email client.
If the email message does not open in your email client, try opening the email client first and then pressing the 'Send by Email' button (security options in your email client may prevent it from being opened by another program - see below) .
If you are using Microsoft Outlook and are prompted to save the message when it first appears, you must click yes.
If when clicking the 'Send by Email' button an error appears with the message 'Unable to send email', it may be because security settings prevent other programs from accessing your email client. To fix this try the following.