问题
I am interested to know the technical background of how this services can determine if my email reached the inbox or not(as this is the key servicethis providers offer). If I send an email to somebody wh uses Yahoo messenger or Gmail or maybe just an enterprise email address, what does the ISP have to do with that? Isn't the email filtered after it reached the Yahoo or Enterprise server, and than moved to Inbox or Junk or whatever other folder?
回答1:
(full disclosure: I currently work for SendGrid as a web developer, so I have some insight but maybe not the low-level technical answers you're seeking)
From a slightly simplistic view, when we go through the SMTP process of delivering a message to an ISP/ESP, we generally know that the message has been "delivered" and we track it as such in your statistics. We also set up feedback loops (FBL's) with ISP's/ESP's which can ping back to us if a user flags a message as spam, which we then subtract from the "delivered" total.
How they route the message and make the decision to move it an Inbox or Junk folder is based on whatever criteria they have, and as far as I know, there is no FBL that can be set up to alert us to that fact.
We do, however, work very hard with our customers to teach them how to "warm up" an IP address for sending good, non-spammy messages, which builds up a "reputation" for an IP address (search google for "sender score"). Obviously the closer to 100% the better. We also have automated systems in place which may alert us if outgoing messages seem "spammy" and we'll put them on hold and alert you so you can make corrections. After all, our reputation is also on the line.
Hope that helps a little.
回答2:
Well, if I recall correctly, SendGrid uses embedded images in the email and tracks if the image gets loaded as a way to determine if the target user read the email. This, of course, is fairly unreliable.
I certainly never allow my email client to automatically show images by default, so the image won't be requested and SendGrid won't be able to count this email as opened.
See these links for more details... now comes the RTFM! :)
- http://docs.sendgrid.com/documentation/apps/click-tracking/
- http://en.wikipedia.org/wiki/Email_tracking
来源：https://stackoverflow.com/questions/9545918/how-software-like-return-path-or-sendgrid-knows-how-many-emails-reached-inbox