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Corrupt Mail App Installation: If the Mail application installation has become corrupt, it may fail to properly communicate with the server and thus fail to download some of the emails messages.Anti-Spam Filtering: If the anti-spam filtering application (like GFI MailEssentials) is editing the emails’ header, making the emails incompatible with the mail application, then the Mail app might show the error at hand.Remove Copy from the Server: If any of your email clients are configured to remove the email copy from the server and it fetches/removes the email from the account before any other client, then other clients may fail to download the message from the server.Outdated OS of Your Device: If your device’s OS is outdated, it may not be compatible with the email server, causing the issue at hand.
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