"The submitted from address () is not valid" error when using SMTP + MimeMail + HTML Email Action

Here's the setup:

1) install smtp & mimemail

2) configure smtp with smtp server, from, etc.

3) configure mimemail to use smtp server

4) create a new rule that uses the mimemail html email action (for example, if content is changed, send an html email... put some html in the email text)

5) do whatever you need to do to trigger the rule in #4 (e.g. edit/save content)

You will see the error: The submitted from address () is not valid

I went in and debugged it and found some missing parentheses in the smtp module.

    if ($from = variable_get('smtp_from', '') == '') {
      // If smtp_from config option is blank, use site_email.
      if ($from = variable_get('site_email', '') == '') {

needs to change to:

    // If from e-mail address is blank, use smtp_from config option.
    if (($from = variable_get('smtp_from', '')) == '') {
      // If smtp_from config option is blank, use site_email.
      if (($from = variable_get('site_email', '')) == '') {

I have attached a patch.

Note that this is a general bug and may come up in other configurations as well but I just saw the issue with this particular configuration.