Configuration settings for non-transactional email

[scottcwilson]

Allows newsletters, product notifications, back in stock mail, abandoned cart mail, etc. to be sent from an SMTP server designed for bulk emailing (rather than your regular email server).

Fixes #3886 as discussed with Chris.

[scottcwilson]

For documentation:

How to test this with your SMTP email server.

• Modify NEWSLETTER_MODULES in Configuration > Email Settings so that the list includes direct_email.
• Go to Customers > Customers and find your account. Press the email button and send yourself a test email.

This email will be delivered by the NEWSLETTER_EMAIL_SMTPAUTH_MAIL_SERVER.

[scottcwilson]

Verified using SendGrid as an external SMTP server.

[scottcwilson]

Verified using Mandrill as an external SMTP server.

[torvista]

Once the upgrade script runs, these email templates
newsletters,product_notification,back_in_stock_notification,recover_cart_sale
will be sent using the credentials in the new fields....but there are none.

Just to be failsafe, should not the script either
copy the existing settings,
or there be a check on sending for the account name being "YourEmailAccountNameHere" / empty, to fallback to the default email settings?

[scottcwilson]

Once the upgrade script runs, these email templates ... will be sent using the credentials in the new fields....but there are none.

This is not correct. See line 215 of includes/functions/functions_email.php

[torvista]

Yes, I see it checks for content in NEWSLETTER_EMAIL_SMTPAUTH_MAIL_SERVER, which is an empty field by default.
Thanks.