Setting up your SPF is a simple two-step process. Let's say you are using "example.com" as a domain.
1) Add the following TXT record to your domain:
Address, Name or Host: example.com
TXT value: v=spf1 mx include:messaging-master.com ~all
If you already have SPF records set up for your domain, just "include:messaging-master.com" to your existing entry.
2) Log into you Critsend account, go to "Account -> Mail Settings" and find the "On Behalf of Addresses" line.
Enter a default email address from the domain you've just updated in step 1, for instance "noreply@example.com". Important: You can have several domains in this field but you can only add ONE "On Behalf of" address per domain. Separate each address from different domains with a comma.
Also note that this is not the same as your Mail-From: or From: address and that it does not affect your Mail-From: or From: address in any way. It will only be used by email providers to check for an appropriate SPF TXT record.
That's it. If you haven't set up your DKIM yet, we recommend that you do it immediately. Read more about how to do it here.
3) Test your settings
Once you've set up your SPF, you can test your domain here. When clicking "Get SPF record", you should see messaging-master.com in the results. (Wait 4 hours for DNS propagation though.)