When you set up Gmail to send mail as your other account, there are two choices:
- Use Gmail's SMTP server
- Use another SMTP server
If you choose the latter option, it should use your real mail server to send the email message. This should produce the same exact email message as if you logged in to your other email host and sent a message from there.
For information on how to use a different SMTP server, see Google's help document. Find the part that says
If you choose to send mail through another domain's SMTP servers.
Google says that this is one of the reasons to use your own SMTP server:
Your Gmail address will still be
included in your email header's sender
field, to help prevent your mail from
being marked as spam. Most email
clients don't display the sender
field, though some versions of
Microsoft Outlook may display "From
email@example.com on behalf of
firstname.lastname@example.org." For this
reason, if you don't want 'on behalf
of' to appear in any of your messages,
we recommend using the SMTP servers of
your other email provider.