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 firstname.lastname@example.org on a website.
The fix is simple, update your SPF record to contain the domain as well, for example:
v=spf1 include:servername.example.com include:_spf.google.com ~all.
As another example, if you are using an email delivery service such as SendGrid, you could enter the IP (if you have a static one):
v=spf1 ip4:18.104.22.168 include:_spf.google.com ~all, or by replacing the domain above with sendgrid.com.
Google does have a KB article on this, but it only mentions IP and not domain. By using the record provided in this example, the IP resolved at the A-Record for the domain example.com will be allowed instead of just the IP.
Note: You do not need to include your top-level domain in the SPF policy, it is automatically assumed