What is owl city's official fan mail address?

Not too sure, but there are ways of contacting him. Apparently.

He wouldn't give away his phone number, although there isa way of contacting him. Sort of.

Head to www.owlcitymusic.com/mobile to see some details and send a text message.

There's apparently a way of calling Owl City himself or something too.

The site said (and I quote) :

Do you have a favourite song on Ocean Eyes?

Call Adam @ 507.216.4583

and tell him about it!

I don't know. Try looking at the site for more details.