People do not receive my emails

People are not receiving my emails. I am receiving other peoples emails. I am using Linux Mint 22 and Thunderbird 140.11.1esr. If I send an email and look in the sent folder, it shows that it has been sent. If I log into my Bell Webmail portal and check the sent folder there, it shows that the email has been sent. But no one gets my emails. If I send an email from my Bell Webmail portal, people receive that email. I have re-installed Thunderbird and allowed Thunderbird to autofil the incoming and outgoing server information after entering my user name and password. No change. I have contacted Bell my internet provider and they have told me that because I can send from the Webmail portal and not from my Desktop, it is a Thunderbird problem. It seems that this problem may have start just after Thunderbird received an update about 2-4 weeks ago. It has been around a month since the last time I had a back and forth email exchange. Searching the forum has been difficult to find an issue similar to mine. Any help would be appreciated. Robert