I am using IMP 4.3.6 and Horde 3.3.6 with Apache 2.2.14 on Ubuntu Server 10.04 (64-bit). As far as I know, everything is working as designed, including S/MIME support.

I am shifting users from a Mozilla Thunderbird IMAP installation to one using IMP. I have found one behavior that I think is probably expected, and if so I would like to understand the implications. If it is not expected, then I would like to resolve my configuration problem (or bug) as is possible.

We use S/MIME for many emails each day. We have used this for years, which means we have tens of thousands of encrypted emails stored for each user. Annually, each email user gets a new digital certificate from Verisign. At that time, the new public key is sent to the other users and encrypted communications continues to be possible. In IMP, it seems that only the most recent public key can be stored at one time. As far as I can tell, older (expired) keys cannot be/are not stored.

This means that emails written with any of the expired keys can never be read again, even though they are not in themselves invalid in any way. They just cannot be decrypted any longer because the proper keys no longer exist in IMP.

On ThunderBird, the certificate/key store retains all of the older expired keys (your own private key/cert as well as the public keys of others). This capability then enables it to continue to decrypt email long after the keys themselves are expired. This is extremely useful and in fact, a bit of a show-stopper for me since we can't afford to lose all archived email each time a key changes.

I have looked through the mailing list archives, the IMP documentation, the Horde/IMP FAQ, google searches... and have also tried to experiment to see if I could get multiple keys stored. As far as I can tell it is not something that can be done and this is not a bug, but just an implementation choice. Is that correct?

If so, is there anything planned in this area in the future (what is the possibility of adding this feature)?

If not, I would appreciate any guidance on how I went wrong.

Best Regards,
Greg Shah

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