Since many older servers do not support 2048 bit keys, we default to using 1024 bit keys. If you would like to send emails to Google and no others, we can easily set up 2048 bit keys, but it is likely that many of the other email providers will reject your emails. As an email marketing platform, our goal is to reach as many people as possible and we wouldn't be able to do that using 2048 bit keys.