[Done 2.0] "Contact Us" Email Dropdown List' when configured throws Error 500

Zen Cart: v1.3.9f-h
Using Heart Internet, everything green during server check during installtion.

Configuring Contacts form email recipients via Admin >> Configuration >> "Contact Us" Email Dropdown List' caused various errors depending what mail transport is being used.

replicated on v1.3.9f-h, first discovered after making changed to cart, then replicated with clean installations.

After providing one or more email addresses for the Contacts Drop down box, and using Sendmail, I got Error 500 upon submitting the form. I tried using SMTP & SMTPAUTH options, this resulted in a server message saying: Email Error: SMTP Error: Could not connect to SMTP host

The relevant server log whilst using Sendmail & the Sendmail-f option said:

**Malformed header from script. Bad header="[email protected]: index.php, referer: http://domain.co.uk/index.php?main_page=contact_us**

Using the default PHP Option I get a slightly diffferent server error:
**Malformed header from script. Bad header=No recipient addresses found i: index.php, referer: http://domains.co.uk/index.php?main_page=contact_us**

As soon as I removed the email address' from the "Contact Us" Email Dropdown List' and saved it blank, PHP & Sendmail & SMTP all worked again.

Did you enter the email addresses as follows:

Name 1 email@address1, Name 2 email@address2

astraios, you're the first person to report those symptoms, and the code driving that hasn't changed significantly in several years.
Thus, it would suggest that it's pointing to a configuration issue with your hosting company's server ... namely overly aggressive mod_security, or similar, rules imposed by the server administrator.

Somewhat-related article: https://www.zen-cart.com/tutorials/index.php?article=63

You must have both elements in Name 1 email@address1, Name 2 email@address2 and it MAY be necessary to have no spaces...

So, something like

Sales[email protected],Returns[email protected]