Is it safe to email an encrypted wallet to myself?
You can trust encryption

If you encrypt anything using a strong key and a strong algorithm (e.g. GPG) then you can be sure that it will be beyond economical reach for anyone for a long time.

So, the general procedure would be


Encrypt wallet.dat with your long and complex passphrase (which you keep safe)
Attach the ciphertext output to your email
Enjoy the free offline backup service


Do not just attach wallet.dat to the email since it will reveal your transaction history and bind your public addresses directly to you thereby removing your anonymity.