email issue with admin gv send and reg email

As this is the only forum marked with email in its title I will post this problem here.

I tried to send a GV to a customer (not a purchased GV, an admin created one) everything seemed to go well, until the customer reported not receiving it. I checked the "gift Certificates Sent" in admin and it wasn't on the list. I went into the DB and it was not list in the coupons table, and the email was not archived in the database.
Troubleshooting this I sent a test GV to myself and it worked, showed up everywhere it is supposed to including my email inbox. I tried sending one to my test account and it appear to work but actually didn't send or register in the DB.
In testing this some more by using the "send email" function in the admin it also failed on the same customers it failed before and worked for the same customers it worked for before. I did note that even though the "email sent" header was green and siad "email sent to : email address here(0)" it didn't send, but I did figure out that if it said "email sent to: email address here(1) then it did actually send.
I was trying to send these emails using the drop down list, if that helps. some would work, some wouldn't. I ended up sending the GV by manually entering the email address in the next line down from the drop down instead of using the dropdown.
What I don't understand is why some of them work and some of them don't, I scanned the DB and I don't see a difference that would be a problem, but maybe I'm not looking at the right tables.
Need anymore info? or do I got everything here.

Do the email addresses that did not get the emails have anything in common? (all freebies? same isp? )

No 1 of them is to a yahoo account that I can send to if I manually enter the email addy instead of using the dropdown and the other one that doesn't work is a test account on the same host as my site.