Invoiceninja: [Feature] Tracking email opens

[Braunson]

I searched previous issues but found no mention of it. It would be helpful to track opens/reads on emails sent out. This could be an optional feature that could be togged globally as well as on a per-client basis and then also manually on the send email view.

[turbo124]

If you use PostMark as your outbound mail provider, then the system has this functionality baked in.

We haven't implemented this for any other mail driver.

[Braunson]

Interesting, I'm using another driver and switching to PostMark specifically to use opens/reads isn't ideal, I'm sure it isn't for other people either. I'll look into modifying the default mail driver in IN to support this by default.

[Braunson]

@turbo124 Is this something you'd accept as a PR if I put one in?

[turbo124]

@Braunson yes we would accept, just PR on the Develop branch :)