Every address you check gets one of four labels. They are color-coded so you can scan your list at a glance.
Safe to send (green)
The address is real and the mailbox is accepting mail. You can send to it with confidence. These are the keepers.
Risky (yellow)
Something about this address is uncertain. It might be fine, but it carries a warning sign — for example, the domain accepts every address it is offered, so we cannot be sure this exact mailbox exists. Send carefully, or hold these back from important sends.
Do not send (red)
The address is not real, or it will bounce. Common reasons: a typo, a made-up address, a throwaway address, or a mailbox that no longer exists. Remove these from your list.
Unknown (grey)
We could not get a clear answer this time — usually because the receiving server was slow or temporarily unavailable. This is not a bad address, just an unfinished one. Try checking it again later.
Tip
A simple rule of thumb: send to green, remove red, and decide case by case on yellow. See "What to do with risky addresses" for help with the yellow ones.
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If you still have a question, we are happy to help.