How do I send messages to users?

Comment on one of their old giveaways or try to contact them over Steam. There is no PM system on this site, unfortunately.

How did he contact you?

Email?

Hello, Sandalwood.

Welcome to the site. The user who complained about never receiving the key left a comment on your giveaway: https://www.steamgifts.com/go/comment/klKj1Vq You can reply to his comment and he will receive a notification.

If you want to communicate with your winner, you can add them to your friend list on Steam, you can send them an email or you can reply to their comment, or leave a comment on their giveaway (if any).

there is a reply button under every comment, if you mean that

@Skibby Thanks. I'll try that.
@HashimotoNanami I sent the gift to them by the e-mail they had listed. If they haven't received it there, I doubt they'd receive a message through it.

@Madumius @SleepyCat http://i.imgur.com/xKbyJxF.png

After a person received a gift, you will get an e-mail from Steam. Title like this: Your Steam gift has been accepted

@moshimoshi Yes, that was the case for the first few entries where the gifts were received without issue. In this case, however, I think I have a user whose e-mail address is out of date or switched Steam accounts. I have no idea.

I left a comment on one of their recent raffles in the hope that they will find it.
I'd still like to figure out why there is no 'reply' feature for me when dealing with comments, though.

Maybe he blacklisted you?

how do I know who blacklisted me?
10+ people blacklisted me