Google advises that when using Apps for e-mail your domain should have a SPF/TXT record with the value v=spf1 include:_spf.google.com ~all.
An issue that may arise is e-mail providers marking the message as spam if you are sending e-mail from your web server as well as google's servers. For example, user account registration validation, contact form submissions, and anything that may come from an address such as noreply@example.com on a website.
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