Knowing the explicit text of the bounce messages might be helpful.

My husband's gmail simply said the delivery was incomplete but it would keep trying. I eventually got it about24 hours later. My daughter's gmail to me bounced back stating the email looked like spam. Others just tell me it gets bounced back.

The actual text may prove helpful. Your response indicated that google thinks your daughter's email is spam.

Hi David, thank you for your help, but I am sorry I am not being clear. She is getting the message that my email appears to be spam, not hers. And others have indicated the same, that their email to me gets bounced back to them indicating that my email is spam.

My confusion is that you are stating that the messages are being returned because your account is spam. Generally, the term 'spam' refers to a message, not to an account. I am puzzled that mail is being bounced back because the account is a spammer, as I don't grasp the reasoning there. But, I don't know everything. You might approach your email provider to investigate why your account is not receiving, as Thunderbird is not in any way a part of that. Your email provider may also ask for the explicit message that senders are receiving, as the actual content of the message might be helpful to them.