Sometimes, I can find the email in question in the search but when I try to open it, it simply shows up blank.

re :I have two deleted folders from two different accounts that keep deleting old emails. It seems that any email with more then a month will get automatically deleted.

Please note: If you are talking about an imap gmail account and emails in the imap 'Trash/Bin/Deleted' (what it is called can vary) folder that are older than 30 days are being deleted, then this is normal. Gmail auto empties/deletes Trash and Spam folders of anything older than 30 days, so they have been deleted off the server.

When you select to read an email in Trash and get blank, it is because it does not exist on server. The Trash index file may be out of synch with server. Right click on 'Trash and select 'Properties' and click on 'Repair folder', click on OK.

Not using a gmail account, its a rented shared server. Tried the 'Repair folder', didn't help. Thanks.

Check to see if there are some settings which might be causing the problem. Do the following for both accounts.

Right click on imap mail account name in Folder Pane and select 'Settings' Select 'Server Settings' At the bottom - Message Storage 'Empty Deleted folder on Exit' - is this checkbox selected ? If yes, uncheck that checkbox.

Worth checking some other settings as well whilst in Account Settings. Click on 'Synchronisation & Storage' Disk Space Select 'Synchronise all messages locally regardless of age' Select 'Don't delete any messages'

Also check the Properties for the actual folder. In Folder Pane Right click on the 'Deleted' folder and select 'Properties' 'General information' tab If you are using 'Global Search' and not finding anything that is still in the 'Trash/Deleted' folder and you would like it to be included... select checkbox: 'Include messages in this folder in Global Search results'

Select 'Retention Policy' tab Either select 'Use my account settings' OR uncheck that option and select 'Don't delete any messages' click on OK

Went over everything. All the settings were properly set, except for one folder that didn't have the checkbox: 'Include messages in this folder in Global Search results'.

Do you think it has to be a problem outside of Thunderbird? From windows or server

Have you actually checked with the server admin what the servers mail system is doing with regard to mail retention and auto deletion. Way back Toad made reference to Google doing automatic deletions, while you may not be using Googles services the industry standards generally see the server doing some automatic emptying of things like the SPAM and trash folders. These server settings override anything set in Thunderbird and are by far the most common cause of mail vanishing from these folders.