New 2048-bit dual CNAME keys for DKIM authentication

We now issue 2048-bit dual CNAME DKIM keys, replacing the 1024-bit single keys. The new keys are more difficult to decrypt, making them a more secure way to authenticate your emails. We've also introduced 2 keys instead of one, which allows us to rotate between the keys without downtime. All new domains will be issued the new keys, and we recommend that you migrate to these new DKIM records for your existing domains.