Can't Get Amazon SES working with vBulletin

[pjkcards]

I'm trying to use Amazon SES for vBulletin after having some complaints about users not getting activation emails, notifications, etc.. In Email Options, I filled in these options:
https://www.dropbox.com/s/hs43eze1vx...59.36.png?dl=0

Using Port 425. I tried both SSL and TLS, and when I do an email diagnostic I get the following message:
"The mailing function returned an error while trying to send the mail."

What else do I need to do to get this working? -f parameter isn't enabled, I've left it as no. Could that cause any issues?

Any help would be greatly appreciated. Thanks.