Internode has revealed it has traded its open source corporate e-mail system for Microsoft's Exchange.
But it was unlikely to make the same underlying changes to its internet customer e-mail service.
Managing director Simon Hackett posted a lengthy justification for the decision on the South Australian ISP's blog today.
"For an organisation with a long history of preference for open source/Unix based systems, and something less than unconditional love for Microsoft, it's an interesting decision," he wrote.
Hackett said the ISP had been trying to get a "working, open-source based, cross-platform calendaring system happening for years and years" but had "never managed" to get it.
Internode users run Windows, Mac and Linux operating systems at the desktop.
"There's always something that doesn't work right, or a need to run a plethora of ‘conduit' tools between multiple calendar systems," he said.
Hackett said he was sold on using Apple's MobileMe service to synchronise e-mail, calendars and contacts ‘over the air' to his iPhone. But it was not a corporate solution.
"For the longest time, in terms of the overall task of moving from simple IMAP email to fully integrated contacts, calendar and e-mail, the piece that didn't ‘click' was the MacOS piece," he said.
But Hackett said the release of Snow Leopard changed everything by "tightly integrating Exchange client functionality into the operating system".
"That was the clincher. We now had all the pieces of the puzzle at last: Exchange Server 2007, Windows Exchange clients, Snow Leopard for exchange integration on MacOS, and easy over the air synchronisation of everything to our iPhone fleet," he said.
"All we had to do was decide that it wasn't illegal, immoral or fattening to trust our e-mail system to Microsoft."
Hackett said still supported secure IMAP in addition to the Outlook specific protocol for mail access (OWA) in Exchange.
"This means our Linux desktop users are able to keep running their weapon of choice (generally Thunderbird) for e-mail access at home and at work after the migration," he said.
Internode also maintained IronPort for spam protection rather than rely on Exchange.
Internode will upgrade to Exchange 2010, which Hackett said the ISP would "move quickly" to.
He said the system was "working better than I'd dared hope".
"Finally, we have the stuff we always wanted, and in the cross-platform manner we've always demanded," Hackett said.
But he believed it unlikely that Internode would transition its customer mail system to Exchange because the service did not need calendar and contacts integration.
"In a world with Google Mail in it, if a customer wants cloud based contacts/calendar/email integration for single user and/or family use, they're quite likely to use that anyway - and for that role, it's brilliant. So why fight it?" he said.