One of the ideas I've tinkered with along the way is hiding encrypted emails in content that's markov generated from unencrypted communications with the same peer. It doesn't have to be perfect, just good enough to not get caught in the slime squad's algorithms.
Or you could send encrypted texts with a subject line that tells how many leading zero bits are in your GPG private key. Perhaps start with keysize - 1.
Then for each new message subtract 1 from the number of leading zeros.
Now at some point Eve has to decide for herself when it's no longer worth it to brute force your messages.
One of the ideas I've tinkered with along the way is hiding encrypted emails in content that's markov generated from unencrypted communications with the same peer. It doesn't have to be perfect, just good enough to not get caught in the slime squad's algorithms.