Thunderbird and copying between IMAP accounts

The Issue
If you have multiple IMAP accounts and wish to copy messages with attachments between the 2 accounts you may find that when you come to open the attachment on the other account that Thunderbird generates the following error message:

This attachment appears to be empty.
Please check with the person who sent this.
Often company firewalls or antivirus programs will destroy attachments.

This blogget will tell you how to overcome this issue and not to panic when it occurs as the attachment did copy across without any issues.

Copying The Message
In Thunderbird messages can be copied between accounts using the following steps.

1. Select [multiple|the] message(s) that you wish to copy to the same folder in another account
2. Right click one of the sselected message(s)
3. Select the Copy To option
4. Then select the Email account you want to copy to
5. Then select further to drill down to the folder you wish to copy the messages to
6. Once at the lowest level of selection the messages will start to copy
7. Your original messages will still remain on the original server

Moving The Message

In Thunderbird messages can be moved between accounts using the following steps.

1. Select [multiple|the] message(s) that you wish to move to the same folder in another account
2. Right click one of the sselected message(s)
3. Select the Move To option
4. Then select the Email account you want to move to
5. Then select further to drill down to the folder you wish to move the messages to
6. Once at the lowest level of selection the messages will start to move
7. Your original messages will be removed from the original server

Shorter Method

1. Select [multiple|the] message(s) that you wish to move to the same folder in another account
2. Click and hold one of the selected messages
3. Drag to the folder on the other account
4. Messages will start to be moved between the accounts
5. Your original messages will be removed from the original server

Looking At The Messages In The New Account

Now select the folder of the account you have just copied the Email messages to, and find one of the Emails that contains an attachment.  When you attempt to view the attachment you will receive the message described at the beginning of this document:

This attachment appears to be empty.
Please check with the person who sent this.
Often company firewalls or antivirus programs will destroy attachments.

Rectifying The Error
Use the following steps to resolve the issue:

1. Right click on the folder
2. Select Properties
3. Click the Repair Folder button
4. Now select a different message and then the one with the attachment
5. Select the attachment and it will now open

Do this for any folder where you receive this error with attacments and you will be able to view them again.  Most of the issues revolve around the MIME boundary being set incorrectly and the repair folder sorts these out so that the attachment can be found again.