Emails retrieved from the "Sent" file have had their messages deleted.
After sending an email it is moved to the "Sent" file. When we need to refer to what message we sent and open the sent email, we find the message is missing. Only a blank field appears. This began about a month ago after several years of proper functionality. Our ISP is SuddenLink.
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This began about a month ago after several years of proper functionality.
What is the size of the Sent file? Did you ever archive sent messages? https://support.mozilla.org/en-US/kb/archived-messages
Do you have a backup in case the missing messages cannot be recovered? http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Backing_Up_and_Restoring
It's possible your mail files are corrupted.
Try to rebuild the index file of the troubled folder. Right-click the folder - Properties - Repair Folder
Note: depending on the corruption this may erase messages from the affected folder which cannot be recovered anymore. In that case you'd need to restore them from a recent backup.
Corruption is often caused by anti-virus software messing with Thunderbird mail files. It is therefore recommended to create an exception for the Thunderbird profile folder, so that the real-time scanner won't attempt to scan the profile with your mail.
For more information on the profile location see http://kb.mozillazine.org/Profile_folder_-_Thunderbird