Hi! I just got latest Avast upgrade and couldn’t Send Emails but could Receive, with Thunderbird. I followed the directions to get rid of old 127.0.0.1 in Outgoing Server SMTP and resort back to my ISP settings. I can now send and receive email. 
Question, I didn’t resort back to ISP settings for each account. I only changed Outgoing Server SMTP. I’m still using the convoluted yourname#pop.slnt.phub.net.cable.rogers.com and 127.0.0.1 for each account name in Thunderbird.
CAN I go back to the regular/old ISP settings for each account name in Thunderbird? I really don’t want to change everything to try it, only to have to go back to original account settings. TX!