If I'm using Gmail, what are the common SMTP settings for Thunderbird and what specific issues might arise?

For Gmail, the common SMTP settings are: Server Name: smtp.gmail.com, Port: 465 (SSL/TLS) or 587 (STARTTLS), Connection security: SSL/TLS or STARTTLS, Authentication method: OAuth2. A common issue is that Gmail requires 'Less secure app access' to be enabled (which Google is phasing out), or you need to use an app-specific password if you have two-factor authentication enabled. Using OAuth2 is the most secure option and avoids using less secure apps or generating an app-specific password.