This is a new problem, started 3 to 4 days ago. I have Outlook 2019 on my Windows 10 PC. I’ve had Avast for many years. Now With Scan Outbound emails checked off, I can’t send mail from Comcast smtp servers. I have uncheck Scan Outbound Emails for the mail to be sent.
New issue
Here is error message attached
My email smtp setting is
I using smtp.comcast.net
Port 465
SSL/TLS
As I stated this only started a couple of days ago.
I have the paid Avast Internet Security program.
Tried avast repair and reboot ?
Thanks, it did help, email was sent after maybe 10 seconds, which seems longer than say godaddy smtp.
Now, still have that same problem, I don’t want to continually do repair for the program. What is the issue
anyone else with comcast? Xfinity?
Turn off Scan Outbound Emails, problem solved 
All mails sent/received are scanned at all mail server they pass thru
I have to, just wondering why it started in the past week.
avast seems to have frequent problems with mail scanning, you are not the first to post about it
Are you sure it’s not the SSL that prevent your email client from incoming and outgoing emails. I know outlook 20007 and newer in combination with avast have that issue and if you turn SSL scanning OFF in avast it all works fine. Usually ISP’s have their own SSL scanning and its enabled in Outlook, try disabling in avast
No incoming issue, it’s the outbound.