Because Accelo will send emails on your behalf, your more security-minded clients can mistakenly mark your emails sent from Accelo as spam! To prevent this from occurring you'll need to add an entry your DNS' SPF record to explicitly define Accelo as an authorized sender of your email.
SPF records are referred to in a couple of different ways depending on your domain host, with the most common terms being SPF Records and TXT Records. You can find more specific information on your domain provider's method for adding SPF records on Google's SPF guide, or you can check Microsoft's SPF Guide. We'll be adding:
to your existing SPF record. If there are no other entries in that SPF record, the completed entry would look like this:
v=spf1 include:_spf.accelo.com ~all
To test your domain's SPF record (and make sure you have Accelo included), use the helpful tool at MXToolbox.com.