I'm operating Thunderbird in a three-year-old DIY 64-bit Windows 7 desktop PC system. I'm the only user of this system and I only created one Comcast cable E-mail address for myself. I've had no need for a second address until now. I'm attempting to use secure online accounts to manage my elderly mother's healthcare. I've found that some sites use E-mail addresses as the sole identification of registered users. I wanted to avoid confusion when I create two accounts at such sites , one for my mother and one for me. I thought I could create a second E-mail address in Thunderbird for my mother, to use when we both have accounts at the same Website. Can this be done in Thunderbird or should I investigate whether my ISP (Comcast) would allow me to create a second address which I can use as my mother's "User ID" at sites which use E-mail addresses for that purpose? Would I be able to receive her mail in Thunderbird? (She doesn't use personal computing technology.)