Evites are not proper etiquette for wedding invitations. Very tacky. Send your guests formal paper invitations. They don't need to be expensive. No, you can't send e-vites through the Knot. Ugh!
If there was to do this, and if this wasn't a bad idea, I would still recommend you not send invitations via TK website. The tools are known for failing and not fuctioning properly.
Re: Is there a way to create a custom outgoing message?
No, you can't send e-vites through the Knot. Ugh!
And also, if I got an email invitation, I probably wouldn't take it seriously.