When sending mail to a recipent with "unrouteable adress" I get a popupwarning. Is it possible to disable this popup?

Question

I am trying to disable a popup alert I get when I send a message to a recipient with an error.
I get the message "Unrouteable adress" as a popup and have to press OK to continue to send mails. The reason I want to disable this is that we are using thunderbird to send out newsletter, and have to press OK on all adresses that is wrong.

Answer 1

Another option is to make an Automator workflow that creates a new email message formatted as you like. Here are the steps:
Open Automator and create a New Service.
Set it to no input in Mail
From the Utilities Library, drag the run Applescript action into the workflow pane.
Copy and paste in this script (replacing what is already there):
property fontName : "Lucida Handwriting"
property fontSize : 14
property fontColor : {14848, 26112, 65535} as RGB color
property emailMessage : "Hello "
on run {input, parameters}
          tell application "Mail"
                    set theMessage to make new outgoing message with properties {visible:true}
                    set the content of theMessage to emailMessage
                    tell content of theMessage
                              set the font to fontName
                              set the size to fontSize
                              set the color to fontColor
                    end tell
          end tell
end run
Change all the Properties to what you want for defaults.
Save the workflow with a useful name.
Open Keyboard System Preferences, Shortcuts menu
Select Services category
Scroll to the bottom section and find you service; select it.
Tab the shortcut field and type the shortcut you want to use. Note that a lot of the N shortcuts are used. I found ctrl-opt-N was free.
Open Mail, go to the Mail menu > Services > name of service
That will open a new mail window. Close it and try the Shortcut.
To get the right color values, you can use the color picker, RGB Slider values multiplied by 256. That's not quite perfect, but it is close. The maximum value is 65535