E-Mail to SMS failure

Hello; I've had this problem kind of before & had posted on here about sending e-mail to my daughters cell phone & was getting blank e-mails back but now my e-mails will send but my daughter doesn't get them & a few days later I'll get the "mail delivery failed" error message, I'm using Thunderbird & not sure what kind of phone she has but she uses T-Mobile, she can send me a message & it comes right through & she has checked her settings & blocked senders list & I'm not on there & "think" it's a T-Mobile thing & no clue how to go through them to see if they have me blocked & from everything I've read it seems to be something with converting e-mail to SMS & I can't find anything in Thunderbird to convert e-mail to SMS when sending. Is there a way in Thunderbird to do that ? Is there a "free" add-on program that will do it without a lot of excess messing around ? I'd like to pretty much just type my message & hit send & have it work right again. I'm fairly advanced with computers but this SMS is something I've never had to deal with before & hope you can explain it better & any ideas on what I can try or if there are any "free" add-on's that will fix the problem. I rely heavily on texting her from my e-mail. Thank you.

 

Hello; I put my daughters phone number at tmomail.net in the send to & then just write a regular e-mail & hit send & it has worked for a long time & then it just quit & by Thunderbird it shows as sent but she doesn't get them now & that seems to be the only part that's not working & after several days I get the "delivery failure" error message. I don't really know if it is an SMS thing but from all my Google searches that's what it keeps suggesting it could be & why I'm going down that road. Thank you