Replied Message Arrow
If an email message has been opened as Reply, but the To address was changed to something else, the Arrow symbol marking Replied items in the Sent folder may still show up for the original message. This might be misleading when browsing Sent items. In some case the user might have had another email address for the same recipient, so the reply would be valid. There can also be cc-recipients on the original message. Also, the user may have changed the whole message, only using the Reply button to "copy" the message to send a new one. Same with forwarding and its arrow symbol.
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