I'm running 60 users, 12 with Blackberry handsets, all configured for IMAP access.
When we were running on SME 6.0 with older hardware (dual PIII 1GHz, 1GB RAM), we found that both Thunderbird and our Blackberry handsets experienced a delay between when an email arrived in the user's inbox and when it would appear in their client; for Thunderbird it was less than 3 minutes, but for the Blackberries it was closer to 15 minutes.
Now that we've upgraded to SME 7.4 with newer hardward (quadcore Xeon 2.5GHz, 8GB RAM), we find that there is an almost instantaneous arrival of email in Thunderbird and on the Blackberry handsets.
While this isn't a bad thing - it's actually made the Blackberries more useful - I'm baffled by how this is possible considering that all Thunderbird clients are set to check for new messages every 10 minutes and all Blackberries (via the BIS website) are also set to check for new messages every 10 minutes. Does this mean that the BB servers are in constant contact with my server, possibly using a significant amount of bandwidth in the process? Am I just paranoid? Should I just be quiet and be happy about it?