They do send emails and make robocalls for some kinds of signal problems, so this may be legitimate. Unfortunately, scammers send similar messages.
You can use webmail to check the authenticity of an email that claims to be from Comcast by looking for the XFINITY Verified Email logo next to the message (see https://www.xfinity.com/support/articles/comcast-verified-email).
You could also check with them using the phone number printed on your bill, or one of the methods listed on the official "Contact Us" page at https://www.xfinity.com/support/contact-us/. That page should list 1-800-Xfinity (1-800-934-6489) or 1-800-Comcast (1-800-266-2278), and a link for Chat: https://support.xfinity.com/chat.
If you haven't scheduled an appointment for repair, please reach out to me and I can get this scheduled for you. No need to call in. To protect the privacy of your account, please send me a private message verifying your first and last name, the phone number, street address including city state and zip code, and the account number associated with your services.
To send a private message click on my name "ComcastChe", then click private message me.