Gmail provides IMAP, but no push. That means: if I get an email at Gmail, Gmail will not notify my iPhone. Instead, I have to configure my iPhone to poll my Gmail account for new messages. I can do that at 15', 30', or 60' intervals, at the cost of some battery.
Yahoo Mail does provide push. So, I now have Gmail forward a duplicate of most emails (except mailing lists, e.g.) to my Yahoo Mail account and the iPhone gets pushes from that one. But if I reply or compose in the Mail app, it will be from my Yahoo address instead of the Gmail one. That's a bit of a bother.
If the situation were reversed – if I preferred Yahoo for my mail and Gmail was the one that pushed – then I could fix this. In the Gmail account on my iPhone, I could set it to use Yahoo's server for outgoing mail. But, as it stands, I cannot do that for the Yahoo account. I can navigate through the Settings menu and even click the "delete this outgoing mail server" button for the Yahoo server, but nothing happens. No explanation: the iPhone just ignores me.
This probably seems mysterious if you're unfamiliar with the territory. Especially since silently ignoring the user is a very bad user interface behavior, and Apple is usually really good at UIs.
The Internet Pessimists claim this is a business move. You see, Apple provides its own push email service as part of
MobileMe. And a MobileMe subscription costs. If I could set my Yahoo account to send via Gmail, I would effect for free the primary feature of MobileMe, push email. But, if I were a Yahoo user, there would be no such issue. The whiners claim that Google, by being a nice partner with Apple, is intentionally not implementing push so as to not compete with MobileMe.
(Putting on my cynic's hat.)
That doesn't make sense to me. The partnership I see is Yahoo and Apple; they're in cahoots to pull (
har) iPhone users away from Gmail.
(Switching to the geek hat.)
For those interested, I currently have to tap three times on each composed message in order to switch the "from" address to my Gmail one. At least I can make it work. Alternatively, the Gmail mobile site works quite well in Mobile Safari, so I go there if I'm planning on composing/replying. The Mail app is really just for me being notified about new emails.
(Switching to the runner hat and grabbing water bottle.)