I think in the case of an evite, they should send the evite to both members of the couple. That way, if it gets filtered out or stuck in the abyss for one person, it hopefully won't have the same thing happen to the other.
Once, a friend sent me an email with a question about something upcoming. Then a week later, they sent me an email complaining that I had not answered the question. I had not received the email. They did not believe me, but we got their question answered and everything was fine.
A few months later, I was checking my email and lo and behold here was the email they had sent me. Somehow, between the day they sent it and the day I received it, it had just been sitting in the internet equivalent of the dead letter office. o, maybe in a few months, you will get the first invitation.