Try deleting the entries in the Mail Shield, Expert Settings, SSL Accounts, reboot and avast should recreate them. Though with no StartTLS, SSL or TLS in the tbird email accounts and the settings in avast it should work, what is the full text of the error message when sending ?
Unfortunately I don’t use thunderbird, so I can’t be much practical help.
only one entry is correct in Avast ssl accounts section >>> SMTP 465 SSL (works with 587 TLS too if that’s gmail). The three other entries are wrong and can’t work: should be IMAP/993/SSL and SMTP 587 TLS (525 doesn’t exist).
now you should give us your settings in Thunderbird and your email provider, Gmail or else…