This might be something obvious that I'm missing.
I would like to have my host encrypt a message to a client using the client's public key, and also have that message signed using the hosts private key.
It seems like an obvious scenario, but perhaps my concept is simply wrong.  I think that you should be able to do with with a single message, much like you see using PGP.  Can this be done with M2Crypto easily?
I tried first encrypting the message and then signing it but I get the message "RSAError: digest too big for rsa key".
I would rather not send the encrypted message and its signature as two separate pieces of data.
Edit:
For the time being I'm using a custom delimiter, to separate the message from the signature, but I feel like this is bad form, and that the format should have provisions for what I'm attempting.
It sounds like you're looking for a hybrid cryptosystem which takes care of encryption and signature together, using appropriate crypto primitives to allow it to work whatever the size of the data, and encapsulating all the components of the cryptogram in one place. PGP, HTTPS and DHIES are good examples. While it seems to me that you could implement such a system using m2crypto, you probably shouldn't; you're much better off reusing an existing protocol than rolling your own. It's far too easy to make mistakes which are hard to spot and render the security useless.
M2Crypto, Encrypt and Sign at once?