I don’t know how avast would get arround your using the SMTP port for secure traffic, avast monitors the email ports 25, 110, 119 and 143 and it is expecting standard email protocols for those ports, it can’t unencrypt SSL traffic to scan it. So there would either be huge delays or possibly this error message being displayed because avast can’t scan SSL.
As I said I don’t use gmail so I can’t say if your setup is correct, I thought that for gmail it used the 587 port.
You might want to do a forum search as this one has come up before where a user had to use SMTP port 25 for secure email and I don’t think it was resolved but that I think was a restriction of their ISP.
This is from a google search about what email ports to use for SSL email:
Generic Settings
* Outgoing Server (SMTP)
* Servername -> mail.yale.edu
* Port -> 587 'Use name and password' or "authentication"
* User Name: netid
*
For SMTP authentication and SSL encryption): Use secure connection TLS or SSL "Always", or "Required"
If you have a client that gives you the choice between SSL and TLS, choose TLS. You want to use port 587 for SMTP. TLS is preferred because it is a more recent standard.
If you not use SSL/TLS by setting this to “Always”, or “Required”, and you are not using POP/Kerberos you are probably sending passwords in clear text between where you are and Yale mailservers. For a discussion of issues with this please see this Information Security Office documentation.
Setting the email client to use port 587 for outbound (SMTP) email, is a way to avoid issues with NAV/SAV version 9 or higher, as wel as Internet providers which prevent sending encrypted data on port 25. Symantec (Norton) Antivirus version 9 (Symantec Anti Virus 9.0.0.338 in PC Amigo and the Software Library) which is the new standard for Windows machines, it does not support SSL or TLS encrypted email via port 25. It is possible to configure NAV/SAV 9 not to autoprotect Internet email -
Configure -> Internet Email Autoprotect-> (Uncheck) Internet Email Autoprotect
It’s less involved to use the Required,Alternate Port: 587.
If you are unable to configure this or have questions about the instructions please contact your support provider.