Short Answer: Yes, but you will need to use a third party addon or program to do so.
In all cases, to send someone else an encrypted message, they will need to share their public key with you. (ie., they must also be set up with an encryption key and be using a compatible client). Otherwise, your only option is to digitally sign your messages. That will add credibility to your messages but will not encrypt them.
This information is to help you get started if you are interested in encrypting your email messages. ILJ Mail can not support or help with encryption as it is done outside of our service and beyond the scope of our provided support. You can view a good Youtube video on the basics of it here: https://youtu.be/AQDCe585Lnc
Mailvelope – Our webmail interface works with Mailvelope which is an addon for your browser. Click here to visit Mailvelope.com to get started. Here’s their tutorial on how to get started: https://www.mailvelope.com/en/help One extra step is that you will need to add webmail.iljmail.com to the approved server list. When you first go to our webmail interface after installing Mailvelope, click the Mailvelope icon and choose “Authorize this domain”. When you are done, refresh the webmail interface and click to compose a new message. You should see the Mailvelope icon there for you to write an encrypted email if you choose.
Thunderbird Email Client – Using the Thunderbird Email Client for encrypted emails means you will also need the Addon called Enigmail. Click here to see how Thunderbird desktop client can digitally sign and encrypt messages with the optional plugin.
Canary Email App (iPhone only as of this writing but the Android app is in early access phase) – this email app seems promising. I am personally using it now and I like it so far. They seem to have a real privacy focus AND they have the ability to encrypt email with any provider. You can either send encrypted email to any other Canary user automatically, or you can import your encryption keys and exchange encrypted emails with other users that are using encryption and compatible email clients or apps. Canary is also available for Mac desktop but I have not tested that. I suggest looking through Canary’s Help Desk to see if this is something you would be interested in. The biggest catch is that it is not free. As of this writing, it’s $20.