About 12 months ago, we stumbled across ClarkConnect and have been using it extensively in deployments of 30 users or less. Felt compelled to reply to the OP since you mention archive and backups.
It has a very simple email archiving module (using MySQL backend).
For backup, we've been using the Bacula module - but the CC team just recently begin offering a remote backup service that is much more elegant.
All in all, one of the best OSS-based platforms for small businesses, IMO.
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About 12 months ago, we stumbled across ClarkConnect and have been using it extensively in deployments of 30 users or less. Felt compelled to reply to the OP since you mention archive and backups.
It has a very simple email archiving module (using MySQL backend).
For backup, we've been using the Bacula module - but the CC team just recently begin offering a remote backup service that is much more elegant.
All in all, one of the best OSS-based platforms for small businesses, IMO.
S.