[thisacctforreal]

4096-bit is likely an RSA key, correct?

Encrypting directly with RSA according to PKCS#1 is limited to a maximum of 501 bytes (key modulus - 11 bytes).

Generally RSA is not used to encrypt data directly, instead you encrypt an AES key with RSA then encrypt the data with that key.

https://stackoverflow.com/a/5586652

https://security.stackexchange.com/a/33445

Edit: the messages are from a character limited contact form so it's fine

[dsr_]

It's an HTTP form sent over TLS.