The file is uploaded and not emailed so SMTP doesn’t come into it.
Send it from the User Files section of the chest (select the file, right click, email to Alwil Software). It will be uploaded (not actually emailed) to avast when the next avast auto (or manual) update is done.
After the normal update completes (if that failed then there may be a knock on effect), then the samples are uploaded, see image.