To Noles315: Sorry about piggy-backing my post that way, but I think we're actually looking for the same thing: You click the phone's built-in email icon or open the email app to send an email from another app, say the contacts app, and the built-in email app would 'take' you the right mail system, whether it uses the built-in email system or your webmail's web-page in the browser.
However, it would be really nice to be able to multiple email sources, and then, when more than one source has been configured, have the app prompt me for the one I want open. If only one address was configured, then the app wouldn't prompt, but instead simply open it.
For aesthetics, I'd have each email account source defined with a 'display name', the current email server information or the URL of the webmail service, if the source is a webmail service. The ‘display names’ would then be shown in the list of email account choices when the user is prompted.
One other possibility would be that webmail sources could have two URLs, one for reading email and the other composing messages and sending them, with the understanding that the composing/sending feature might not be supported by all webmail services. The composing/sending address would be used when the another app calls the email app, so the user would be able to skip the webmail site’s email list and begin creating the email immediately, provided the service supports this. If the service doesn’t then both URL could be the same or lacking a second URL the first would be assumed.