How is it that some recipients are shown in different colors?

When looking the eevid details at the user site, most recipients appear in green color but others are shown in red or yellow. What do these colors stand for?

Given the recipient's address is correct, we will very likely succeed on delivering your emails. Sometimes, however, it may take us a while or we may completely fail to do so. These colors tell you at which stage of delivery an email is.

• Gray, standing for pending delivery. On average, it takes us about 3 seconds to process and deliver an email. While in the process of being delivered, emails will show up in gray color. Unlike most mail servers, we won't retry delivery for too long: if we can't deliver your email within the next two hours, we will cancel it and send you a postmaster error message to warn you. Whilst grayed, no further action is required on your side.
• Red, standing for failed delivery. If we haven't been able to deliver your email, it will be listed in red. When faced with a failed delivery, take a look at the postmaster error message we will have sent you and get to know what the non-delivery reason is. Based on this, it's up to you to try sending it again.
• Green, standing for confirmed delivery. Email delivery for that recipient has been successful and the evidence receipt has been issued.
• Yellow, standing for deferred message received after confirmed delivery. Your email has been successfully delivered and registered, but a deferred message from the recipient's mail server has been received afterwards. Such deferred messages may inform of a real delivery problem or merely result from an out-of-office's auto-reply setting at destination. We will keep record of any deferred message we get and pass it on to you for you to decide whether it requires further action.