I can send emails from my email address firstname.lastname@example.org but can't receive emails even when they are directly replied to by the receiver.
Hello JAndryski and welcome,
According to the following domain information this is not a Comcast supported domain:
This is especially true in that your above MX and NS records have no Comcast email or website records information. This means you need to contact your email server hosting company for resolution to your issue.
If you need to use your existing tricom1.com email under the Comcast unbrella, please follow these Use your existing domain name with Comcast Business email and web hosting instructions.
Hope this helps you out.