Iphone: outgoing email iCloud account and gmail
You can setup your iCloud account to send using the Gmail SMTP server.

Setting =&gt; Mail, Contacts, Calendar =&gt; iCloud =&gt; Account =&gt; Advanced (Mail) =&gt; Outgoing mail server (SMTP) =&gt; Other SMTP Serveres =&gt; Add Server here you can set up the Gmail SMTP server: smtp.gmail.com - remember to choose the Gmail server, and de-activate the iCloud SMTP server afterwards.

The mails sent will however appear in iCloud's sent folder.

The iCloud sender email address will however still be the iCloud address. If you use the build in Mail.app, you can manually choose your Gmail address (and the mail will appear in Gmail's sent folder), but how you can use this one, the way you want to use it - I don't know.