Corrupted attachments in Mail.app connecting to an IMAP server

Question

Hi,
I'm using Mail.app to connect to our local IMAP server (over SSL). For a long while, I've had problems with large attachments being corrupted when I open a message in Mail. If I view the same message in our webmail client (which also talks to the IMAP server), the attachments are uncorrupted.
If I save a message as source and decode using a mime64 decoding tool, the attachments are corrupted in the same way as from within mail. This is most clearly visible when the attachment is a large jpeg.
If I remove the locally cached messages by deleting the /Library/Mail/IMAP-xxxxx folder, then re-download all the messages, the attachments will be often corrupted in a different position in the image.
Using another IMAP mail client (Thunderbird) on the same machine to connect to the same IMAP server shows no corruption in the same messages which are corrupted in Mail.app.
I can't say whether this problem was introduced with Tiger, but it has persisted for a long time. This problem is only for INCOMING attachments; I have had no problems with corruption in the attachments I send to others.
Other Tiger Mail.app users in the building have the same issue. Any suggestions to identify and fix this problem will be greatly appreciated. It's possible it's bug in Mail, and I would be happy to contribute any information or perform any testing required to fix it.
Using:
Mail.app v2.1 (752/752.2)
Thunderbird v1.5.0.7 (20060909)
Mac OS X 10.4.8 Build 8L127
1 Ghz Powerbook G4 with 1.25 GB RAM
Best regards,
Dylan
Powerbook G4 Mac OS X (10.4.8)
Powerbook G4   Mac OS X (10.4.8)  

Answer 1

The right way of doing that would be rebuilding the
mailbox, i.e. select it and do Mailbox >
Rebuild. Does that make a difference?
Rebuilding the mailbox — no difference. The attachments are corrupted at a different position in the image, but still corrupted.
Another thing to try would be trashing the Mail
cache, i.e., quit Mail, in the Finder go to
Trashing the Mail Cache — no difference. The attachments are not re-downloaded from the server, and so the position of the corruption in the image doesn't change.
What happens if you move or copy the message to a
local "On My Mac" mailbox, and open the local copy
instead?
The local copy then has corrupted attachments.
/Library/StartupItems/
Empty.
/Library/InputManagers/
SIMBL
~/Library/InputManagers/
Empty.
/Library/Mail/Bundles/
Empty.
~/Library/Mail/Bundles/
GPGMail
Mail.appetizer
A quick test — disabling these plug-in components has no effect on the corrupted messages, even after re-building the mailbox in question.
I should point out again that it's not just my machine that's affected by this problem. I verified today that other users of the same server are also affected. This isn't likely to be caused by a quirky configuration on my machine.
Also, open System Preferences, and go to
Accounts > Login Items. What do you see
there?
LittleSnitchDaemon
iCalAlarmScheduler
iCal
Mail
SmartReporter
LiteSwitchX
MicrosoftMouseHelper
MouseLocatorAgent
Skype
Last.fm
Renicer
The items below the line have been added recently, and the problem was definitely there before hand.
Dylan.
Powerbook G4   Mac OS X (10.4.8)