Gmail: Send Email Without “on behalf of”
One of the great thing about Gmail is that it lets you send emails as if they were from your non-Gmail addresses. There’s just one problem, it adds the words “on behalf of” and displays your Gmail address in the “From” area. Of course this is one of the reasons to use Google Apps for Domains as it will let you send emails from your domain without adding any such text.
Now you can acheive the same in Gmail and Google Apps. You will need to provide your non-Gmail email address’s server address (SMTP), username and password as Google will use this to send the mails in future.
Here’s what Google has to say:
Since these messages are sent by Gmail’s servers but “from” a non-Gmail address, we have to include your original Gmail username in the “Sender” field of the message header to comply with mail delivery protocols and help prevent your mail from being marked as spam. Most email programs just display the “From” address and not the “Sender” field, but some (including versions of Microsoft Outlook) show these messages as coming “From username@gmail.com On Behalf Of customaddress@mydomain.com” which really annoyed people.
via Official Gmail Blog.