Depends on what for computer you can use for it. There are probably many simple mailservers for such a purpose. You might even choose to use only a program where your Epson can connect to without TLS and where the program connects to the mailserver of your choice, such as outlook.com. For example, stunnel could do something like that. Assuming you can only set up a single mailserver in your Epson though.
In any case, as I've said numerous times before, this is the Let's Encrypt Community which is rather specifically meant to help people with their Let's Encrypt issues. I still feel this Community is not meant for "Setting up my Epson printer" issues if it's not directly Let's Encrypt related.