Rated 4 out of 5 stars
Although the extension did not work at first, it appeared to be a configuration related problem. In the account settings, you can select which SMTP server must be used for the specified account. If this entry is not set to "Use Default Server", the extension will not have any effect.
A small request: is it possible to provide an option to set whether the default SMTP server should be changed or whether the message should just be send for this time by an alternative SMTP server.
Thank you very much for this extension!