If you’re a gmail user, you probably know by now you can set a custom “from” address instead of just the “reply-to” (see under Settings… Accounts). It makes it possible to use Gmail with your existing mail address both for incoming and outgoing mail, without other people even noticing. Still, there are some issues:
For outgoing mail, Gmail adds an extra Sender: email@example.com header, I assume as an anti-spam measure. Mailing list software like ezmlm also take this sender header into account when checking membership (any useful mailinglist requires subscription beforehand, again an anti-spam measure), so mail sent via Gmail gets rejected, even with an access-entitled From: (and Reply-to:).
Another problem, as reported by Christopher Schulte, is that outlook 2003 treats the Sender: as the real sender “on behalf of” the From:, and he suggests
I hope they modify the system to replace Sender: with something far less intrusive like X-Googlemail-Userid: which would both preserve the identifiable gmail account information (making abuse complaints far easier to manage) and put the customized domain back up front and center.
Still, Gmail remains a fantastic mail client and archive… I still use it side by side with Outlook mail folders, where I store items that unambiguously belong under some project. All the rest “disappears” (labeled according to some filter rules) in Gmail’s archive, ready to be retrieved by some well-formulated full-text search. I can imagine people relying on it entirely even for professional purposes (and even companies – when will google start to offer hosted corporate mail?)…